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 $63.44   12.570%   $71.4144   $71.41   $71.40   $71.40  
  Purchase #2 $133.35   4.391%   $139.2054   $139.21   $139.20   $139.20  
  Purchase #3 $212.47   3.587%   $220.0913   $220.09   $220.10   $220.10  
  Purchase #4 $236.58   7.774%   $254.9717   $254.97   $254.95   $255.00  
  Purchase #5 $156.27   8.557%   $169.642   $169.64   $169.65   $169.60  
  Purchase #6 $224.34   5.614%   $236.9344   $236.93   $236.95   $236.90  
  Purchase #7 $214.74   9.435%   $235.0007   $235.00   $235.00   $235.00  
  7 purchase totals = $1,241.19       $1,327.2599   $1,327.25   $1,327.25   $1,327.20