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 $92.86   11.638%   $103.667   $103.67   $103.65   $103.70  
  Purchase #2 $151.26   12.555%   $170.2507   $170.25   $170.25   $170.30  
  Purchase #3 $54.60   11.108%   $60.665   $60.67   $60.65   $60.70  
  Purchase #4 $21.74   4.232%   $22.66   $22.66   $22.65   $22.70  
  Purchase #5 $247.77   7.808%   $267.1159   $267.12   $267.10   $267.10  
  Purchase #6 $42.82   4.616%   $44.7966   $44.80   $44.80   $44.80  
  Purchase #7 $161.79   3.556%   $167.5433   $167.54   $167.55   $167.50  
  7 purchase totals = $772.84       $836.6985   $836.71   $836.65   $836.80