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 $228.98   10.191%   $252.3154   $252.32   $252.30   $252.30  
  Purchase #2 $149.77   11.321%   $166.7255   $166.73   $166.75   $166.70  
  Purchase #3 $129.32   9.365%   $141.4308   $141.43   $141.45   $141.40  
  Purchase #4 $223.88   8.868%   $243.7337   $243.73   $243.75   $243.70  
  Purchase #5 $31.70   12.300%   $35.5991   $35.60   $35.60   $35.60  
  Purchase #6 $163.56   5.645%   $172.793   $172.79   $172.80   $172.80  
  Purchase #7 $19.86   8.660%   $21.5799   $21.58   $21.60   $21.60  
  7 purchase totals = $947.07       $1,034.1774   $1,034.18   $1,034.25   $1,034.10