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 $206.61   13.199%   $233.8805   $233.88   $233.90   $233.90  
  Purchase #2 $15.96   7.334%   $17.1305   $17.13   $17.15   $17.10  
  Purchase #3 $228.67   7.127%   $244.9673   $244.97   $244.95   $245.00  
  Purchase #4 $206.78   9.400%   $226.2173   $226.22   $226.20   $226.20  
  Purchase #5 $94.91   3.576%   $98.304   $98.30   $98.30   $98.30  
  Purchase #6 $126.25   5.218%   $132.8377   $132.84   $132.85   $132.80  
  Purchase #7 $220.27   6.811%   $235.2726   $235.27   $235.25   $235.30  
  7 purchase totals = $1,099.45       $1,188.6099   $1,188.61   $1,188.60   $1,188.60