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 $97.63   3.705%   $101.2472   $101.25   $101.25   $101.20  
  Purchase #2 $118.25   4.620%   $123.7132   $123.71   $123.70   $123.70  
  Purchase #3 $110.86   13.178%   $125.4691   $125.47   $125.45   $125.50  
  Purchase #4 $167.61   10.217%   $184.7347   $184.73   $184.75   $184.70  
  Purchase #5 $231.80   4.110%   $241.327   $241.33   $241.35   $241.30  
  Purchase #6 $155.27   10.566%   $171.6758   $171.68   $171.70   $171.70  
  Purchase #7 $244.82   12.672%   $275.8436   $275.84   $275.85   $275.80  
  7 purchase totals = $1,126.24       $1,224.0106   $1,224.01   $1,224.05   $1,223.90