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 $30.52   11.494%   $34.028   $34.03   $34.05   $34.00  
  Purchase #2 $18.84   7.117%   $20.1808   $20.18   $20.20   $20.20  
  Purchase #3 $105.62   3.790%   $109.623   $109.62   $109.60   $109.60  
  Purchase #4 $71.43   3.605%   $74.0051   $74.01   $74.00   $74.00  
  Purchase #5 $67.48   6.305%   $71.7346   $71.73   $71.75   $71.70  
  Purchase #6 $69.96   3.317%   $72.2806   $72.28   $72.30   $72.30  
  Purchase #7 $62.49   10.418%   $69.0002   $69.00   $69.00   $69.00  
  7 purchase totals = $426.34       $450.8523   $450.85   $450.90   $450.80