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 $225.95   6.721%   $241.1361   $241.14   $241.15   $241.10  
  Purchase #2 $210.74   8.395%   $228.4316   $228.43   $228.45   $228.40  
  Purchase #3 $74.30   3.772%   $77.1026   $77.10   $77.10   $77.10  
  Purchase #4 $215.57   13.474%   $244.6159   $244.62   $244.60   $244.60  
  Purchase #5 $168.79   13.666%   $191.8568   $191.86   $191.85   $191.90  
  Purchase #6 $246.91   9.337%   $269.964   $269.96   $269.95   $270.00  
  Purchase #7 $237.27   3.577%   $245.7571   $245.76   $245.75   $245.80  
  7 purchase totals = $1,379.53       $1,498.8641   $1,498.87   $1,498.85   $1,498.90