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 $58.88   8.438%   $63.8483   $63.85   $63.85   $63.80  
  Purchase #2 $228.42   5.355%   $240.6519   $240.65   $240.65   $240.70  
  Purchase #3 $46.90   12.868%   $52.9351   $52.94   $52.95   $52.90  
  Purchase #4 $29.55   9.468%   $32.3478   $32.35   $32.35   $32.30  
  Purchase #5 $237.92   9.479%   $260.4724   $260.47   $260.45   $260.50  
  Purchase #6 $139.80   11.233%   $155.5037   $155.50   $155.50   $155.50  
  Purchase #7 $165.67   3.406%   $171.3127   $171.31   $171.30   $171.30  
  7 purchase totals = $907.14       $977.0719   $977.07   $977.05   $977.00