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 $57.93   12.829%   $65.3618   $65.36   $65.35   $65.40  
  Purchase #2 $240.73   5.807%   $254.7092   $254.71   $254.70   $254.70  
  Purchase #3 $81.70   7.787%   $88.062   $88.06   $88.05   $88.10  
  Purchase #4 $25.86   9.413%   $28.2942   $28.29   $28.30   $28.30  
  Purchase #5 $193.65   11.787%   $216.4755   $216.48   $216.50   $216.50  
  Purchase #6 $151.83   5.446%   $160.0987   $160.10   $160.10   $160.10  
  Purchase #7 $197.78   6.307%   $210.254   $210.25   $210.25   $210.30  
  7 purchase totals = $949.48       $1,023.2554   $1,023.25   $1,023.25   $1,023.40