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 $46.44   6.572%   $49.492   $49.49   $49.50   $49.50  
  Purchase #2 $131.52   9.184%   $143.5988   $143.60   $143.60   $143.60  
  Purchase #3 $165.99   9.316%   $181.4536   $181.45   $181.45   $181.50  
  Purchase #4 $72.29   6.244%   $76.8038   $76.80   $76.80   $76.80  
  Purchase #5 $226.32   13.188%   $256.1671   $256.17   $256.15   $256.20  
  Purchase #6 $30.26   13.382%   $34.3094   $34.31   $34.30   $34.30  
  Purchase #7 $200.27   4.419%   $209.1199   $209.12   $209.10   $209.10  
  7 purchase totals = $873.09       $950.9446   $950.94   $950.90   $951.00