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 $217.73   12.527%   $245.005   $245.01   $245.00   $245.00  
  Purchase #2 $147.99   9.204%   $161.611   $161.61   $161.60   $161.60  
  Purchase #3 $62.37   13.392%   $70.7226   $70.72   $70.70   $70.70  
  Purchase #4 $244.29   13.405%   $277.0371   $277.04   $277.05   $277.00  
  Purchase #5 $129.95   9.226%   $141.9392   $141.94   $141.95   $141.90  
  Purchase #6 $205.52   11.710%   $229.5864   $229.59   $229.60   $229.60  
  Purchase #7 $100.26   8.458%   $108.74   $108.74   $108.75   $108.70  
  7 purchase totals = $1,108.11       $1,234.6413   $1,234.65   $1,234.65   $1,234.50