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 $70.35   6.754%   $75.1014   $75.10   $75.10   $75.10  
  Purchase #2 $209.84   6.438%   $223.3495   $223.35   $223.35   $223.30  
  Purchase #3 $109.37   3.388%   $113.0755   $113.08   $113.10   $113.10  
  Purchase #4 $8.67   8.500%   $9.407   $9.41   $9.40   $9.40  
  Purchase #5 $22.65   11.394%   $25.2307   $25.23   $25.25   $25.20  
  Purchase #6 $94.69   7.285%   $101.5882   $101.59   $101.60   $101.60  
  Purchase #7 $232.28   7.594%   $249.9193   $249.92   $249.90   $249.90  
  7 purchase totals = $747.85       $797.6716   $797.68   $797.70   $797.60