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 $98.62   4.254%   $102.8153   $102.82   $102.80   $102.80  
  Purchase #2 $44.68   12.312%   $50.181   $50.18   $50.20   $50.20  
  Purchase #3 $77.63   11.839%   $86.8206   $86.82   $86.80   $86.80  
  Purchase #4 $159.65   9.738%   $175.1967   $175.20   $175.20   $175.20  
  Purchase #5 $212.52   6.455%   $226.2382   $226.24   $226.25   $226.20  
  Purchase #6 $216.53   9.329%   $236.7301   $236.73   $236.75   $236.70  
  Purchase #7 $206.80   9.666%   $226.7893   $226.79   $226.80   $226.80  
  7 purchase totals = $1,016.43       $1,104.7712   $1,104.78   $1,104.80   $1,104.70