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 $84.55   12.156%   $94.8279   $94.83   $94.85   $94.80  
  Purchase #2 $229.54   11.285%   $255.4436   $255.44   $255.45   $255.40  
  Purchase #3 $197.85   13.162%   $223.891   $223.89   $223.90   $223.90  
  Purchase #4 $110.29   3.505%   $114.1557   $114.16   $114.15   $114.20  
  Purchase #5 $218.52   12.795%   $246.4796   $246.48   $246.50   $246.50  
  Purchase #6 $24.25   9.543%   $26.5642   $26.56   $26.55   $26.60  
  Purchase #7 $113.92   4.726%   $119.3039   $119.30   $119.30   $119.30  
  7 purchase totals = $978.92       $1,080.6659   $1,080.66   $1,080.70   $1,080.70