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 $161.42   12.260%   $181.2101   $181.21   $181.20   $181.20  
  Purchase #2 $181.52   12.726%   $204.6202   $204.62   $204.60   $204.60  
  Purchase #3 $160.37   9.313%   $175.3053   $175.31   $175.30   $175.30  
  Purchase #4 $46.33   5.554%   $48.9032   $48.90   $48.90   $48.90  
  Purchase #5 $145.70   4.122%   $151.7058   $151.71   $151.70   $151.70  
  Purchase #6 $172.39   8.424%   $186.9121   $186.91   $186.90   $186.90  
  Purchase #7 $18.31   4.149%   $19.0697   $19.07   $19.05   $19.10  
  7 purchase totals = $886.04       $967.7264   $967.73   $967.65   $967.70