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 $79.84   4.179%   $83.1765   $83.18   $83.20   $83.20  
  Purchase #2 $193.34   5.772%   $204.4996   $204.50   $204.50   $204.50  
  Purchase #3 $177.45   13.596%   $201.5761   $201.58   $201.60   $201.60  
  Purchase #4 $25.26   8.444%   $27.393   $27.39   $27.40   $27.40  
  Purchase #5 $232.51   7.342%   $249.5809   $249.58   $249.60   $249.60  
  Purchase #6 $31.73   12.608%   $35.7305   $35.73   $35.75   $35.70  
  Purchase #7 $71.72   3.127%   $73.9627   $73.96   $73.95   $74.00  
  7 purchase totals = $811.85       $875.9193   $875.92   $876.00   $876.00