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 $184.94   9.398%   $202.3207   $202.32   $202.30   $202.30  
  Purchase #2 $23.44   13.459%   $26.5948   $26.59   $26.60   $26.60  
  Purchase #3 $114.32   4.688%   $119.6793   $119.68   $119.70   $119.70  
  Purchase #4 $87.93   5.473%   $92.7424   $92.74   $92.75   $92.70  
  Purchase #5 $137.53   5.373%   $144.9195   $144.92   $144.90   $144.90  
  Purchase #6 $82.43   6.829%   $88.0591   $88.06   $88.05   $88.10  
  Purchase #7 $68.46   7.289%   $73.45   $73.45   $73.45   $73.50  
  7 purchase totals = $699.05       $747.7658   $747.76   $747.75   $747.80