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 $39.26   4.556%   $41.0487   $41.05   $41.05   $41.00  
  Purchase #2 $45.82   4.805%   $48.0217   $48.02   $48.00   $48.00  
  Purchase #3 $160.29   10.831%   $177.651   $177.65   $177.65   $177.70  
  Purchase #4 $232.59   4.870%   $243.9171   $243.92   $243.90   $243.90  
  Purchase #5 $112.59   6.857%   $120.3103   $120.31   $120.30   $120.30  
  Purchase #6 $80.88   4.328%   $84.3805   $84.38   $84.40   $84.40  
  Purchase #7 $6.34   5.712%   $6.7021   $6.70   $6.70   $6.70  
  7 purchase totals = $677.77       $722.0314   $722.03   $722.00   $722.00