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 $191.35   8.280%   $207.1938   $207.19   $207.20   $207.20  
  Purchase #2 $155.75   4.756%   $163.1575   $163.16   $163.15   $163.20  
  Purchase #3 $230.96   4.239%   $240.7504   $240.75   $240.75   $240.80  
  Purchase #4 $93.66   4.310%   $97.6967   $97.70   $97.70   $97.70  
  Purchase #5 $70.32   10.374%   $77.615   $77.62   $77.60   $77.60  
  Purchase #6 $123.75   6.244%   $131.477   $131.48   $131.50   $131.50  
  Purchase #7 $104.57   8.865%   $113.8401   $113.84   $113.85   $113.80  
  7 purchase totals = $970.36       $1,031.7305   $1,031.74   $1,031.75   $1,031.80