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 $239.43   10.793%   $265.2717   $265.27   $265.25   $265.30  
  Purchase #2 $70.59   5.394%   $74.3976   $74.40   $74.40   $74.40  
  Purchase #3 $75.44   11.375%   $84.0213   $84.02   $84.00   $84.00  
  Purchase #4 $164.48   10.207%   $181.2685   $181.27   $181.25   $181.30  
  Purchase #5 $118.47   5.191%   $124.6198   $124.62   $124.60   $124.60  
  Purchase #6 $205.49   9.749%   $225.5232   $225.52   $225.50   $225.50  
  Purchase #7 $94.94   12.335%   $106.6508   $106.65   $106.65   $106.70  
  7 purchase totals = $968.84       $1,061.7529   $1,061.75   $1,061.65   $1,061.80