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 $61.72   4.260%   $64.3493   $64.35   $64.35   $64.30  
  Purchase #2 $217.48   8.433%   $235.8201   $235.82   $235.80   $235.80  
  Purchase #3 $248.89   8.828%   $270.862   $270.86   $270.85   $270.90  
  Purchase #4 $214.39   3.780%   $222.4939   $222.49   $222.50   $222.50  
  Purchase #5 $22.51   11.552%   $25.1104   $25.11   $25.10   $25.10  
  Purchase #6 $238.35   6.279%   $253.316   $253.32   $253.30   $253.30  
  Purchase #7 $235.29   9.277%   $257.1179   $257.12   $257.10   $257.10  
  7 purchase totals = $1,238.63       $1,329.0696   $1,329.07   $1,329.00   $1,329.00