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 $167.94   5.598%   $177.3413   $177.34   $177.35   $177.30  
  Purchase #2 $218.49   6.329%   $232.3182   $232.32   $232.30   $232.30  
  Purchase #3 $66.73   7.174%   $71.5172   $71.52   $71.50   $71.50  
  Purchase #4 $92.87   4.857%   $97.3807   $97.38   $97.40   $97.40  
  Purchase #5 $77.84   5.369%   $82.0192   $82.02   $82.00   $82.00  
  Purchase #6 $97.68   8.623%   $106.1029   $106.10   $106.10   $106.10  
  Purchase #7 $160.50   4.455%   $167.6503   $167.65   $167.65   $167.70  
  7 purchase totals = $882.05       $934.3298   $934.33   $934.30   $934.30