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 $117.93   10.484%   $130.2938   $130.29   $130.30   $130.30  
  Purchase #2 $216.98   13.515%   $246.3048   $246.30   $246.30   $246.30  
  Purchase #3 $177.33   13.792%   $201.7874   $201.79   $201.80   $201.80  
  Purchase #4 $244.59   9.149%   $266.9675   $266.97   $266.95   $267.00  
  Purchase #5 $178.59   7.305%   $191.636   $191.64   $191.65   $191.60  
  Purchase #6 $51.46   12.803%   $58.0484   $58.05   $58.05   $58.00  
  Purchase #7 $83.49   3.259%   $86.2109   $86.21   $86.20   $86.20  
  7 purchase totals = $1,070.37       $1,181.2488   $1,181.25   $1,181.25   $1,181.20