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 $204.66   6.420%   $217.7992   $217.80   $217.80   $217.80  
  Purchase #2 $68.85   3.307%   $71.1269   $71.13   $71.15   $71.10  
  Purchase #3 $219.52   11.294%   $244.3126   $244.31   $244.30   $244.30  
  Purchase #4 $203.33   9.457%   $222.5589   $222.56   $222.55   $222.60  
  Purchase #5 $209.41   3.753%   $217.2692   $217.27   $217.25   $217.30  
  Purchase #6 $240.26   11.104%   $266.9385   $266.94   $266.95   $266.90  
  Purchase #7 $243.56   9.757%   $267.3241   $267.32   $267.30   $267.30  
  7 purchase totals = $1,389.59       $1,507.3294   $1,507.33   $1,507.30   $1,507.30