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 $135.59   12.582%   $152.6499   $152.65   $152.65   $152.60  
  Purchase #2 $250.46   13.517%   $284.3147   $284.31   $284.30   $284.30  
  Purchase #3 $20.54   6.768%   $21.9301   $21.93   $21.95   $21.90  
  Purchase #4 $241.73   5.862%   $255.9002   $255.90   $255.90   $255.90  
  Purchase #5 $119.42   13.277%   $135.2754   $135.28   $135.30   $135.30  
  Purchase #6 $221.91   8.585%   $240.961   $240.96   $240.95   $241.00  
  Purchase #7 $24.80   4.618%   $25.9453   $25.95   $25.95   $25.90  
  7 purchase totals = $1,014.45       $1,116.9766   $1,116.98   $1,117.00   $1,116.90