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 $87.67   5.567%   $92.5506   $92.55   $92.55   $92.60  
  Purchase #2 $102.71   10.817%   $113.8201   $113.82   $113.80   $113.80  
  Purchase #3 $228.60   8.370%   $247.7338   $247.73   $247.75   $247.70  
  Purchase #4 $215.96   13.874%   $245.9223   $245.92   $245.90   $245.90  
  Purchase #5 $238.68   5.237%   $251.1797   $251.18   $251.20   $251.20  
  Purchase #6 $54.45   12.436%   $61.2214   $61.22   $61.20   $61.20  
  Purchase #7 $177.48   13.409%   $201.2783   $201.28   $201.30   $201.30  
  7 purchase totals = $1,105.55       $1,213.7062   $1,213.70   $1,213.70   $1,213.70