Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.90   12.120%   $151.2499   $151.25   $151.25   $151.20  
  Purchase #2 $146.79   10.206%   $161.7714   $161.77   $161.75   $161.80  
  Purchase #3 $195.27   4.146%   $203.3659   $203.37   $203.35   $203.40  
  Purchase #4 $170.41   5.586%   $179.9291   $179.93   $179.95   $179.90  
  Purchase #5 $145.85   4.663%   $152.651   $152.65   $152.65   $152.70  
  Purchase #6 $122.58   12.143%   $137.4649   $137.46   $137.45   $137.50  
  Purchase #7 $109.89   9.112%   $119.9032   $119.90   $119.90   $119.90  
  7 purchase totals = $1,025.69       $1,106.3354   $1,106.33   $1,106.30   $1,106.40