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 $62.82   3.825%   $65.2229   $65.22   $65.20   $65.20  
  Purchase #2 $99.30   5.162%   $104.4259   $104.43   $104.45   $104.40  
  Purchase #3 $235.70   6.161%   $250.2215   $250.22   $250.20   $250.20  
  Purchase #4 $146.58   12.544%   $164.967   $164.97   $164.95   $165.00  
  Purchase #5 $180.55   13.448%   $204.8304   $204.83   $204.85   $204.80  
  Purchase #6 $243.33   10.833%   $269.6899   $269.69   $269.70   $269.70  
  Purchase #7 $100.47   6.603%   $107.104   $107.10   $107.10   $107.10  
  7 purchase totals = $1,068.75       $1,166.4616   $1,166.46   $1,166.45   $1,166.40