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 $184.41   9.299%   $201.5583   $201.56   $201.55   $201.60  
  Purchase #2 $79.31   11.619%   $88.525   $88.53   $88.55   $88.50  
  Purchase #3 $71.42   8.502%   $77.4921   $77.49   $77.50   $77.50  
  Purchase #4 $21.28   13.162%   $24.0809   $24.08   $24.10   $24.10  
  Purchase #5 $197.83   5.753%   $209.2112   $209.21   $209.20   $209.20  
  Purchase #6 $46.99   10.317%   $51.838   $51.84   $51.85   $51.80  
  Purchase #7 $43.71   9.702%   $47.9507   $47.95   $47.95   $48.00  
  7 purchase totals = $644.95       $700.6562   $700.66   $700.70   $700.70