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 $57.48   5.708%   $60.761   $60.76   $60.75   $60.80  
  Purchase #2 $31.55   6.214%   $33.5105   $33.51   $33.50   $33.50  
  Purchase #3 $228.28   12.319%   $256.4018   $256.40   $256.40   $256.40  
  Purchase #4 $141.75   10.252%   $156.2822   $156.28   $156.30   $156.30  
  Purchase #5 $69.95   6.573%   $74.5478   $74.55   $74.55   $74.50  
  Purchase #6 $20.25   12.485%   $22.7782   $22.78   $22.80   $22.80  
  Purchase #7 $181.87   3.564%   $188.3518   $188.35   $188.35   $188.40  
  7 purchase totals = $731.13       $792.6333   $792.63   $792.65   $792.70