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 $244.96   7.454%   $263.2193   $263.22   $263.20   $263.20  
  Purchase #2 $118.98   11.490%   $132.6508   $132.65   $132.65   $132.70  
  Purchase #3 $43.26   3.210%   $44.6486   $44.65   $44.65   $44.60  
  Purchase #4 $64.76   10.390%   $71.4886   $71.49   $71.50   $71.50  
  Purchase #5 $110.89   7.348%   $119.0382   $119.04   $119.05   $119.00  
  Purchase #6 $93.79   3.587%   $97.1542   $97.15   $97.15   $97.20  
  Purchase #7 $192.74   7.148%   $206.5171   $206.52   $206.50   $206.50  
  7 purchase totals = $869.38       $934.7168   $934.72   $934.70   $934.70