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 $250.56   8.562%   $272.0129   $272.01   $272.00   $272.00  
  Purchase #2 $31.67   5.302%   $33.3491   $33.35   $33.35   $33.30  
  Purchase #3 $207.92   10.333%   $229.4044   $229.40   $229.40   $229.40  
  Purchase #4 $108.48   11.779%   $121.2579   $121.26   $121.25   $121.30  
  Purchase #5 $104.78   8.131%   $113.2997   $113.30   $113.30   $113.30  
  Purchase #6 $174.93   13.686%   $198.8709   $198.87   $198.85   $198.90  
  Purchase #7 $76.25   8.413%   $82.6649   $82.66   $82.65   $82.70  
  7 purchase totals = $954.59       $1,050.8598   $1,050.85   $1,050.80   $1,050.90