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 $241.82   11.478%   $269.5761   $269.58   $269.60   $269.60  
  Purchase #2 $101.35   3.276%   $104.6702   $104.67   $104.65   $104.70  
  Purchase #3 $103.77   7.589%   $111.6451   $111.65   $111.65   $111.60  
  Purchase #4 $118.71   5.372%   $125.0871   $125.09   $125.10   $125.10  
  Purchase #5 $66.61   13.598%   $75.6676   $75.67   $75.65   $75.70  
  Purchase #6 $36.60   13.224%   $41.44   $41.44   $41.45   $41.40  
  Purchase #7 $129.91   6.510%   $138.3671   $138.37   $138.35   $138.40  
  7 purchase totals = $798.77       $866.4532   $866.47   $866.45   $866.50