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 $116.33   11.522%   $129.7335   $129.73   $129.75   $129.70  
  Purchase #2 $202.85   11.790%   $226.766   $226.77   $226.75   $226.80  
  Purchase #3 $82.70   4.504%   $86.4248   $86.42   $86.40   $86.40  
  Purchase #4 $110.38   6.761%   $117.8428   $117.84   $117.85   $117.80  
  Purchase #5 $208.38   8.731%   $226.5737   $226.57   $226.55   $226.60  
  Purchase #6 $134.46   6.527%   $143.2362   $143.24   $143.25   $143.20  
  Purchase #7 $86.88   7.764%   $93.6254   $93.63   $93.65   $93.60  
  7 purchase totals = $941.98       $1,024.2024   $1,024.20   $1,024.20   $1,024.10