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 $206.97   12.482%   $232.804   $232.80   $232.80   $232.80  
  Purchase #2 $53.34   9.359%   $58.3321   $58.33   $58.35   $58.30  
  Purchase #3 $32.53   12.591%   $36.6259   $36.63   $36.65   $36.60  
  Purchase #4 $204.52   10.805%   $226.6184   $226.62   $226.60   $226.60  
  Purchase #5 $22.50   13.701%   $25.5827   $25.58   $25.60   $25.60  
  Purchase #6 $41.77   8.261%   $45.2206   $45.22   $45.20   $45.20  
  Purchase #7 $105.62   11.377%   $117.6364   $117.64   $117.65   $117.60  
  7 purchase totals = $667.25       $742.8201   $742.82   $742.85   $742.70