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 $23.47   9.263%   $25.644   $25.64   $25.65   $25.60  
  Purchase #2 $100.58   10.292%   $110.9317   $110.93   $110.95   $110.90  
  Purchase #3 $199.85   6.456%   $212.7523   $212.75   $212.75   $212.80  
  Purchase #4 $183.43   7.293%   $196.8075   $196.81   $196.80   $196.80  
  Purchase #5 $107.93   11.610%   $120.4607   $120.46   $120.45   $120.50  
  Purchase #6 $76.86   6.860%   $82.1326   $82.13   $82.15   $82.10  
  Purchase #7 $203.99   4.251%   $212.6616   $212.66   $212.65   $212.70  
  7 purchase totals = $896.11       $961.3904   $961.38   $961.40   $961.40