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 $45.72   6.236%   $48.5711   $48.57   $48.55   $48.60  
  Purchase #2 $43.63   13.676%   $49.5968   $49.60   $49.60   $49.60  
  Purchase #3 $60.72   11.314%   $67.5899   $67.59   $67.60   $67.60  
  Purchase #4 $205.79   6.283%   $218.7198   $218.72   $218.70   $218.70  
  Purchase #5 $26.49   9.489%   $29.0036   $29.00   $29.00   $29.00  
  Purchase #6 $247.37   13.434%   $280.6017   $280.60   $280.60   $280.60  
  Purchase #7 $102.71   4.796%   $107.636   $107.64   $107.65   $107.60  
  7 purchase totals = $732.43       $801.7189   $801.72   $801.70   $801.70