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 $181.62   10.804%   $201.2422   $201.24   $201.25   $201.20  
  Purchase #2 $130.57   12.541%   $146.9448   $146.94   $146.95   $146.90  
  Purchase #3 $142.51   7.710%   $153.4975   $153.50   $153.50   $153.50  
  Purchase #4 $94.48   12.283%   $106.085   $106.09   $106.10   $106.10  
  Purchase #5 $238.40   5.558%   $251.6503   $251.65   $251.65   $251.70  
  Purchase #6 $59.79   11.859%   $66.8805   $66.88   $66.90   $66.90  
  Purchase #7 $123.53   6.545%   $131.615   $131.62   $131.60   $131.60  
  7 purchase totals = $970.90       $1,057.9153   $1,057.92   $1,057.95   $1,057.90