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 $43.26   12.682%   $48.7462   $48.75   $48.75   $48.70  
  Purchase #2 $210.44   8.152%   $227.5951   $227.60   $227.60   $227.60  
  Purchase #3 $121.48   13.425%   $137.7887   $137.79   $137.80   $137.80  
  Purchase #4 $190.50   6.278%   $202.4596   $202.46   $202.45   $202.50  
  Purchase #5 $197.62   9.254%   $215.9078   $215.91   $215.90   $215.90  
  Purchase #6 $152.87   9.483%   $167.3667   $167.37   $167.35   $167.40  
  Purchase #7 $14.87   12.769%   $16.7688   $16.77   $16.75   $16.80  
  7 purchase totals = $931.04       $1,016.6329   $1,016.65   $1,016.60   $1,016.70