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 $41.35   5.820%   $43.7566   $43.76   $43.75   $43.80  
  Purchase #2 $215.32   7.765%   $232.0396   $232.04   $232.05   $232.00  
  Purchase #3 $60.52   6.737%   $64.5972   $64.60   $64.60   $64.60  
  Purchase #4 $210.67   3.381%   $217.7928   $217.79   $217.80   $217.80  
  Purchase #5 $244.44   6.523%   $260.3848   $260.38   $260.40   $260.40  
  Purchase #6 $243.38   8.664%   $264.4664   $264.47   $264.45   $264.50  
  Purchase #7 $210.27   13.228%   $238.0845   $238.08   $238.10   $238.10  
  7 purchase totals = $1,225.95       $1,321.1219   $1,321.12   $1,321.15   $1,321.20