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 $192.94   11.762%   $215.6336   $215.63   $215.65   $215.60  
  Purchase #2 $74.83   13.123%   $84.6499   $84.65   $84.65   $84.60  
  Purchase #3 $135.29   11.164%   $150.3938   $150.39   $150.40   $150.40  
  Purchase #4 $168.38   5.693%   $177.9659   $177.97   $177.95   $178.00  
  Purchase #5 $91.41   10.465%   $100.9761   $100.98   $101.00   $101.00  
  Purchase #6 $103.85   6.853%   $110.9668   $110.97   $110.95   $111.00  
  Purchase #7 $30.27   10.294%   $33.386   $33.39   $33.40   $33.40  
  7 purchase totals = $796.97       $873.9721   $873.98   $874.00   $874.00