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 $192.93   7.160%   $206.7438   $206.74   $206.75   $206.70  
  Purchase #2 $144.95   3.789%   $150.4422   $150.44   $150.45   $150.40  
  Purchase #3 $202.99   12.271%   $227.8989   $227.90   $227.90   $227.90  
  Purchase #4 $78.54   5.126%   $82.566   $82.57   $82.55   $82.60  
  Purchase #5 $53.64   3.661%   $55.6038   $55.60   $55.60   $55.60  
  Purchase #6 $14.36   3.348%   $14.8408   $14.84   $14.85   $14.80  
  Purchase #7 $205.29   12.254%   $230.4462   $230.45   $230.45   $230.40  
  7 purchase totals = $892.70       $968.5417   $968.54   $968.55   $968.40