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 $69.53   10.482%   $76.8181   $76.82   $76.80   $76.80  
  Purchase #2 $83.78   12.844%   $94.5407   $94.54   $94.55   $94.50  
  Purchase #3 $155.67   7.476%   $167.3079   $167.31   $167.30   $167.30  
  Purchase #4 $167.62   13.253%   $189.8347   $189.83   $189.85   $189.80  
  Purchase #5 $69.32   6.596%   $73.8923   $73.89   $73.90   $73.90  
  Purchase #6 $56.52   12.238%   $63.4369   $63.44   $63.45   $63.40  
  Purchase #7 $244.88   6.320%   $260.3564   $260.36   $260.35   $260.40  
  7 purchase totals = $847.32       $926.1870   $926.19   $926.20   $926.10