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 $57.97   13.529%   $65.8128   $65.81   $65.80   $65.80  
  Purchase #2 $168.91   8.787%   $183.7521   $183.75   $183.75   $183.80  
  Purchase #3 $150.69   7.761%   $162.3851   $162.39   $162.40   $162.40  
  Purchase #4 $30.72   7.799%   $33.1159   $33.12   $33.10   $33.10  
  Purchase #5 $216.35   9.106%   $236.0508   $236.05   $236.05   $236.10  
  Purchase #6 $52.90   4.217%   $55.1308   $55.13   $55.15   $55.10  
  Purchase #7 $27.74   7.171%   $29.7292   $29.73   $29.75   $29.70  
  7 purchase totals = $705.28       $765.9767   $765.98   $766.00   $766.00