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 $54.41   7.694%   $58.5963   $58.60   $58.60   $58.60  
  Purchase #2 $102.68   6.613%   $109.4702   $109.47   $109.45   $109.50  
  Purchase #3 $231.57   6.863%   $247.4626   $247.46   $247.45   $247.50  
  Purchase #4 $62.41   11.623%   $69.6639   $69.66   $69.65   $69.70  
  Purchase #5 $100.42   10.452%   $110.9159   $110.92   $110.90   $110.90  
  Purchase #6 $159.94   4.615%   $167.3212   $167.32   $167.30   $167.30  
  Purchase #7 $47.52   10.357%   $52.4416   $52.44   $52.45   $52.40  
  7 purchase totals = $758.95       $815.8717   $815.87   $815.80   $815.90