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 $101.65   6.700%   $108.4606   $108.46   $108.45   $108.50  
  Purchase #2 $168.30   4.422%   $175.7422   $175.74   $175.75   $175.70  
  Purchase #3 $41.48   6.339%   $44.1094   $44.11   $44.10   $44.10  
  Purchase #4 $166.69   8.807%   $181.3704   $181.37   $181.35   $181.40  
  Purchase #5 $45.80   12.761%   $51.6445   $51.64   $51.65   $51.60  
  Purchase #6 $209.72   10.130%   $230.9646   $230.96   $230.95   $231.00  
  Purchase #7 $229.28   5.155%   $241.0994   $241.10   $241.10   $241.10  
  7 purchase totals = $962.92       $1,033.3911   $1,033.38   $1,033.35   $1,033.40