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 $56.25   6.160%   $59.715   $59.72   $59.70   $59.70  
  Purchase #2 $181.47   13.464%   $205.9031   $205.90   $205.90   $205.90  
  Purchase #3 $74.72   12.725%   $84.2281   $84.23   $84.25   $84.20  
  Purchase #4 $55.33   5.212%   $58.2138   $58.21   $58.20   $58.20  
  Purchase #5 $131.70   9.272%   $143.9112   $143.91   $143.90   $143.90  
  Purchase #6 $130.99   5.363%   $138.015   $138.02   $138.00   $138.00  
  Purchase #7 $55.95   7.381%   $60.0797   $60.08   $60.10   $60.10  
  7 purchase totals = $686.41       $750.0659   $750.07   $750.05   $750.00