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 $178.87   10.635%   $197.8928   $197.89   $197.90   $197.90  
  Purchase #2 $129.76   9.166%   $141.6538   $141.65   $141.65   $141.70  
  Purchase #3 $201.32   6.415%   $214.2347   $214.23   $214.25   $214.20  
  Purchase #4 $32.77   11.644%   $36.5857   $36.59   $36.60   $36.60  
  Purchase #5 $41.49   8.627%   $45.0693   $45.07   $45.05   $45.10  
  Purchase #6 $116.27   3.247%   $120.0453   $120.05   $120.05   $120.00  
  Purchase #7 $213.73   7.390%   $229.5246   $229.52   $229.50   $229.50  
  7 purchase totals = $914.21       $985.0062   $985.00   $985.00   $985.00