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 $98.49   13.481%   $111.7674   $111.77   $111.75   $111.80  
  Purchase #2 $205.96   13.481%   $233.7255   $233.73   $233.75   $233.70  
  Purchase #3 $90.39   13.355%   $102.4616   $102.46   $102.45   $102.50  
  Purchase #4 $245.99   4.658%   $257.4482   $257.45   $257.45   $257.40  
  Purchase #5 $18.85   4.292%   $19.659   $19.66   $19.65   $19.70  
  Purchase #6 $206.71   6.370%   $219.8774   $219.88   $219.90   $219.90  
  Purchase #7 $138.70   3.454%   $143.4907   $143.49   $143.50   $143.50  
  7 purchase totals = $1,005.09       $1,088.4298   $1,088.44   $1,088.45   $1,088.50