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 $54.98   6.481%   $58.5433   $58.54   $58.55   $58.50  
  Purchase #2 $57.88   8.133%   $62.5874   $62.59   $62.60   $62.60  
  Purchase #3 $159.80   13.714%   $181.715   $181.72   $181.70   $181.70  
  Purchase #4 $139.53   9.208%   $152.3779   $152.38   $152.40   $152.40  
  Purchase #5 $9.88   11.835%   $11.0493   $11.05   $11.05   $11.00  
  Purchase #6 $197.33   7.219%   $211.5753   $211.58   $211.60   $211.60  
  Purchase #7 $66.93   10.371%   $73.8713   $73.87   $73.85   $73.90  
  7 purchase totals = $686.33       $751.7195   $751.73   $751.75   $751.70