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 $141.44   6.467%   $150.5869   $150.59   $150.60   $150.60  
  Purchase #2 $34.48   6.415%   $36.6919   $36.69   $36.70   $36.70  
  Purchase #3 $224.60   7.401%   $241.2226   $241.22   $241.20   $241.20  
  Purchase #4 $208.73   6.185%   $221.64   $221.64   $221.65   $221.60  
  Purchase #5 $146.92   12.153%   $164.7752   $164.78   $164.80   $164.80  
  Purchase #6 $159.68   9.390%   $174.674   $174.67   $174.65   $174.70  
  Purchase #7 $233.40   4.415%   $243.7046   $243.70   $243.70   $243.70  
  7 purchase totals = $1,149.25       $1,233.2952   $1,233.29   $1,233.30   $1,233.30