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 $46.41   12.283%   $52.1105   $52.11   $52.10   $52.10  
  Purchase #2 $80.33   6.769%   $85.7675   $85.77   $85.75   $85.80  
  Purchase #3 $245.43   9.786%   $269.4478   $269.45   $269.45   $269.40  
  Purchase #4 $102.38   9.350%   $111.9525   $111.95   $111.95   $112.00  
  Purchase #5 $5.84   10.531%   $6.455   $6.46   $6.45   $6.50  
  Purchase #6 $117.50   3.647%   $121.7852   $121.79   $121.80   $121.80  
  Purchase #7 $91.53   13.553%   $103.9351   $103.94   $103.95   $103.90  
  7 purchase totals = $689.42       $751.4536   $751.47   $751.45   $751.50