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 $157.73   3.682%   $163.5376   $163.54   $163.55   $163.50  
  Purchase #2 $203.92   4.264%   $212.6151   $212.62   $212.60   $212.60  
  Purchase #3 $14.61   5.139%   $15.3608   $15.36   $15.35   $15.40  
  Purchase #4 $176.48   9.773%   $193.7274   $193.73   $193.75   $193.70  
  Purchase #5 $184.59   10.477%   $203.9295   $203.93   $203.95   $203.90  
  Purchase #6 $215.27   4.753%   $225.5018   $225.50   $225.50   $225.50  
  Purchase #7 $60.65   6.320%   $64.4831   $64.48   $64.50   $64.50  
  7 purchase totals = $1,013.25       $1,079.1553   $1,079.16   $1,079.20   $1,079.10