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 $246.84   11.250%   $274.6095   $274.61   $274.60   $274.60  
  Purchase #2 $123.62   8.635%   $134.2946   $134.29   $134.30   $134.30  
  Purchase #3 $117.27   9.259%   $128.128   $128.13   $128.15   $128.10  
  Purchase #4 $71.83   7.647%   $77.3228   $77.32   $77.30   $77.30  
  Purchase #5 $182.34   6.691%   $194.5404   $194.54   $194.55   $194.50  
  Purchase #6 $20.50   8.698%   $22.2831   $22.28   $22.30   $22.30  
  Purchase #7 $212.98   3.870%   $221.2223   $221.22   $221.20   $221.20  
  7 purchase totals = $975.38       $1,052.4007   $1,052.39   $1,052.40   $1,052.30