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 $151.27   9.290%   $165.323   $165.32   $165.30   $165.30  
  Purchase #2 $215.52   13.747%   $245.1475   $245.15   $245.15   $245.10  
  Purchase #3 $69.99   6.732%   $74.7017   $74.70   $74.70   $74.70  
  Purchase #4 $56.25   8.393%   $60.9711   $60.97   $60.95   $61.00  
  Purchase #5 $213.41   13.229%   $241.642   $241.64   $241.65   $241.60  
  Purchase #6 $94.52   9.136%   $103.1553   $103.16   $103.15   $103.20  
  Purchase #7 $37.54   12.432%   $42.207   $42.21   $42.20   $42.20  
  7 purchase totals = $838.50       $933.1476   $933.15   $933.10   $933.10