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 $213.58   10.648%   $236.322   $236.32   $236.30   $236.30  
  Purchase #2 $83.67   9.120%   $91.3007   $91.30   $91.30   $91.30  
  Purchase #3 $77.96   11.479%   $86.909   $86.91   $86.90   $86.90  
  Purchase #4 $37.44   4.755%   $39.2203   $39.22   $39.20   $39.20  
  Purchase #5 $203.58   12.851%   $229.7421   $229.74   $229.75   $229.70  
  Purchase #6 $244.76   8.860%   $266.4457   $266.45   $266.45   $266.40  
  Purchase #7 $43.48   12.450%   $48.8933   $48.89   $48.90   $48.90  
  7 purchase totals = $904.47       $998.8331   $998.83   $998.80   $998.70