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 $92.97   3.810%   $96.5122   $96.51   $96.50   $96.50  
  Purchase #2 $106.92   9.735%   $117.3287   $117.33   $117.35   $117.30  
  Purchase #3 $71.67   4.192%   $74.6744   $74.67   $74.65   $74.70  
  Purchase #4 $145.76   6.118%   $154.6776   $154.68   $154.70   $154.70  
  Purchase #5 $240.63   8.618%   $261.3675   $261.37   $261.35   $261.40  
  Purchase #6 $22.92   7.558%   $24.6523   $24.65   $24.65   $24.70  
  Purchase #7 $205.88   11.456%   $229.4656   $229.47   $229.45   $229.50  
  7 purchase totals = $886.75       $958.6783   $958.68   $958.65   $958.80