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 $58.57   9.480%   $64.1224   $64.12   $64.10   $64.10  
  Purchase #2 $161.97   4.395%   $169.0886   $169.09   $169.10   $169.10  
  Purchase #3 $37.91   9.104%   $41.3613   $41.36   $41.35   $41.40  
  Purchase #4 $204.28   3.458%   $211.344   $211.34   $211.35   $211.30  
  Purchase #5 $208.96   3.626%   $216.5369   $216.54   $216.55   $216.50  
  Purchase #6 $231.43   10.639%   $256.0518   $256.05   $256.05   $256.10  
  Purchase #7 $57.63   10.505%   $63.684   $63.68   $63.70   $63.70  
  7 purchase totals = $960.75       $1,022.1890   $1,022.18   $1,022.20   $1,022.20