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 $212.57   6.208%   $225.7663   $225.77   $225.75   $225.80  
  Purchase #2 $50.55   11.251%   $56.2374   $56.24   $56.25   $56.20  
  Purchase #3 $46.90   8.151%   $50.7228   $50.72   $50.70   $50.70  
  Purchase #4 $183.96   6.523%   $195.9597   $195.96   $195.95   $196.00  
  Purchase #5 $141.96   13.636%   $161.3177   $161.32   $161.30   $161.30  
  Purchase #6 $204.52   7.677%   $220.221   $220.22   $220.20   $220.20  
  Purchase #7 $140.28   7.576%   $150.9076   $150.91   $150.90   $150.90  
  7 purchase totals = $980.74       $1,061.1325   $1,061.14   $1,061.05   $1,061.10