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 $62.77   4.409%   $65.5375   $65.54   $65.55   $65.50  
  Purchase #2 $244.76   5.453%   $258.1068   $258.11   $258.10   $258.10  
  Purchase #3 $210.74   6.779%   $225.0261   $225.03   $225.05   $225.00  
  Purchase #4 $12.93   3.334%   $13.3611   $13.36   $13.35   $13.40  
  Purchase #5 $212.37   5.631%   $224.3286   $224.33   $224.35   $224.30  
  Purchase #6 $56.69   4.364%   $59.164   $59.16   $59.15   $59.20  
  Purchase #7 $75.32   7.237%   $80.7709   $80.77   $80.75   $80.80  
  7 purchase totals = $875.58       $926.2950   $926.30   $926.30   $926.30