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 $225.95   3.154%   $233.0765   $233.08   $233.10   $233.10  
  Purchase #2 $216.76   13.659%   $246.3672   $246.37   $246.35   $246.40  
  Purchase #3 $156.46   11.179%   $173.9507   $173.95   $173.95   $174.00  
  Purchase #4 $72.32   7.359%   $77.642   $77.64   $77.65   $77.60  
  Purchase #5 $5.81   4.171%   $6.0523   $6.05   $6.05   $6.10  
  Purchase #6 $195.30   4.489%   $204.067   $204.07   $204.05   $204.10  
  Purchase #7 $35.59   10.712%   $39.4024   $39.40   $39.40   $39.40  
  7 purchase totals = $908.19       $980.5581   $980.56   $980.55   $980.70