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 $23.32   8.113%   $25.212   $25.21   $25.20   $25.20  
  Purchase #2 $245.43   11.717%   $274.187   $274.19   $274.20   $274.20  
  Purchase #3 $224.39   10.178%   $247.2284   $247.23   $247.25   $247.20  
  Purchase #4 $247.46   10.451%   $273.322   $273.32   $273.30   $273.30  
  Purchase #5 $8.41   3.102%   $8.6709   $8.67   $8.65   $8.70  
  Purchase #6 $8.89   10.258%   $9.8019   $9.80   $9.80   $9.80  
  Purchase #7 $135.57   10.676%   $150.0435   $150.04   $150.05   $150.00  
  7 purchase totals = $893.47       $988.4657   $988.46   $988.45   $988.40