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 $24.97   4.496%   $26.0927   $26.09   $26.10   $26.10  
  Purchase #2 $222.56   9.343%   $243.3538   $243.35   $243.35   $243.40  
  Purchase #3 $245.61   13.771%   $279.433   $279.43   $279.45   $279.40  
  Purchase #4 $232.43   3.573%   $240.7347   $240.73   $240.75   $240.70  
  Purchase #5 $246.83   3.171%   $254.657   $254.66   $254.65   $254.70  
  Purchase #6 $162.88   12.562%   $183.341   $183.34   $183.35   $183.30  
  Purchase #7 $90.48   8.417%   $98.0957   $98.10   $98.10   $98.10  
  7 purchase totals = $1,225.76       $1,325.7079   $1,325.70   $1,325.75   $1,325.70