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 $222.54   8.113%   $240.5947   $240.59   $240.60   $240.60  
  Purchase #2 $110.67   7.445%   $118.9094   $118.91   $118.90   $118.90  
  Purchase #3 $98.73   3.112%   $101.8025   $101.80   $101.80   $101.80  
  Purchase #4 $13.25   5.392%   $13.9644   $13.96   $13.95   $14.00  
  Purchase #5 $28.95   6.302%   $30.7744   $30.77   $30.75   $30.80  
  Purchase #6 $192.52   6.779%   $205.5709   $205.57   $205.55   $205.60  
  Purchase #7 $151.82   7.804%   $163.668   $163.67   $163.65   $163.70  
  7 purchase totals = $818.48       $875.2843   $875.27   $875.20   $875.40