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 $236.43   8.141%   $255.6778   $255.68   $255.70   $255.70  
  Purchase #2 $194.32   8.457%   $210.7536   $210.75   $210.75   $210.80  
  Purchase #3 $196.51   4.298%   $204.956   $204.96   $204.95   $205.00  
  Purchase #4 $152.57   8.644%   $165.7582   $165.76   $165.75   $165.80  
  Purchase #5 $34.34   12.829%   $38.7455   $38.75   $38.75   $38.70  
  Purchase #6 $16.26   6.597%   $17.3327   $17.33   $17.35   $17.30  
  Purchase #7 $230.42   12.811%   $259.9391   $259.94   $259.95   $259.90  
  7 purchase totals = $1,060.85       $1,153.1629   $1,153.17   $1,153.20   $1,153.20