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 $114.55   13.223%   $129.6969   $129.70   $129.70   $129.70  
  Purchase #2 $241.56   3.717%   $250.5388   $250.54   $250.55   $250.50  
  Purchase #3 $52.25   5.218%   $54.9764   $54.98   $55.00   $55.00  
  Purchase #4 $161.47   11.163%   $179.4949   $179.49   $179.50   $179.50  
  Purchase #5 $99.46   3.468%   $102.9093   $102.91   $102.90   $102.90  
  Purchase #6 $27.34   8.665%   $29.709   $29.71   $29.70   $29.70  
  Purchase #7 $232.25   12.160%   $260.4916   $260.49   $260.50   $260.50  
  7 purchase totals = $928.88       $1,007.8169   $1,007.82   $1,007.85   $1,007.80