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 $48.78   7.669%   $52.5209   $52.52   $52.50   $52.50  
  Purchase #2 $203.78   6.329%   $216.6772   $216.68   $216.70   $216.70  
  Purchase #3 $133.92   10.860%   $148.4637   $148.46   $148.45   $148.50  
  Purchase #4 $185.45   6.781%   $198.0254   $198.03   $198.05   $198.00  
  Purchase #5 $199.72   12.361%   $224.4074   $224.41   $224.40   $224.40  
  Purchase #6 $152.73   4.189%   $159.1279   $159.13   $159.15   $159.10  
  Purchase #7 $48.72   9.838%   $53.5131   $53.51   $53.50   $53.50  
  7 purchase totals = $973.10       $1,052.7356   $1,052.74   $1,052.75   $1,052.70