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 $216.82   13.861%   $246.8734   $246.87   $246.85   $246.90  
  Purchase #2 $30.82   11.221%   $34.2783   $34.28   $34.30   $34.30  
  Purchase #3 $247.86   10.555%   $274.0216   $274.02   $274.00   $274.00  
  Purchase #4 $44.62   5.668%   $47.1491   $47.15   $47.15   $47.10  
  Purchase #5 $137.38   9.829%   $150.8831   $150.88   $150.90   $150.90  
  Purchase #6 $220.88   5.592%   $233.2316   $233.23   $233.25   $233.20  
  Purchase #7 $24.98   5.323%   $26.3097   $26.31   $26.30   $26.30  
  7 purchase totals = $923.36       $1,012.7468   $1,012.74   $1,012.75   $1,012.70