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 $194.91   13.869%   $221.9421   $221.94   $221.95   $221.90  
  Purchase #2 $212.42   10.806%   $235.3741   $235.37   $235.35   $235.40  
  Purchase #3 $22.25   10.371%   $24.5575   $24.56   $24.55   $24.60  
  Purchase #4 $169.60   11.327%   $188.8106   $188.81   $188.80   $188.80  
  Purchase #5 $45.78   10.282%   $50.4871   $50.49   $50.50   $50.50  
  Purchase #6 $232.51   9.286%   $254.1009   $254.10   $254.10   $254.10  
  Purchase #7 $218.82   6.469%   $232.9755   $232.98   $233.00   $233.00  
  7 purchase totals = $1,096.29       $1,208.2478   $1,208.25   $1,208.25   $1,208.30