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 $202.66   4.871%   $212.5316   $212.53   $212.55   $212.50  
  Purchase #2 $81.98   6.865%   $87.6079   $87.61   $87.60   $87.60  
  Purchase #3 $96.45   9.332%   $105.4507   $105.45   $105.45   $105.50  
  Purchase #4 $206.36   6.557%   $219.891   $219.89   $219.90   $219.90  
  Purchase #5 $182.77   11.729%   $204.2071   $204.21   $204.20   $204.20  
  Purchase #6 $212.60   9.873%   $233.59   $233.59   $233.60   $233.60  
  Purchase #7 $218.38   4.526%   $228.2639   $228.26   $228.25   $228.30  
  7 purchase totals = $1,201.20       $1,291.5422   $1,291.54   $1,291.55   $1,291.60