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 $105.77   12.339%   $118.821   $118.82   $118.80   $118.80  
  Purchase #2 $50.53   5.629%   $53.3743   $53.37   $53.35   $53.40  
  Purchase #3 $23.69   7.741%   $25.5238   $25.52   $25.50   $25.50  
  Purchase #4 $215.79   10.517%   $238.4846   $238.48   $238.50   $238.50  
  Purchase #5 $117.52   5.605%   $124.107   $124.11   $124.10   $124.10  
  Purchase #6 $228.34   6.217%   $242.5359   $242.54   $242.55   $242.50  
  Purchase #7 $165.57   10.538%   $183.0178   $183.02   $183.00   $183.00  
  7 purchase totals = $907.21       $985.8644   $985.86   $985.80   $985.80