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 $66.93   7.126%   $71.6994   $71.70   $71.70   $71.70  
  Purchase #2 $208.71   11.480%   $232.6699   $232.67   $232.65   $232.70  
  Purchase #3 $195.52   4.794%   $204.8932   $204.89   $204.90   $204.90  
  Purchase #4 $26.73   6.651%   $28.5078   $28.51   $28.50   $28.50  
  Purchase #5 $52.55   3.149%   $54.2048   $54.20   $54.20   $54.20  
  Purchase #6 $164.75   12.457%   $185.2729   $185.27   $185.25   $185.30  
  Purchase #7 $142.44   4.829%   $149.3184   $149.32   $149.30   $149.30  
  7 purchase totals = $857.63       $926.5664   $926.56   $926.50   $926.60