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 $206.93   8.264%   $224.0307   $224.03   $224.05   $224.00  
  Purchase #2 $220.87   6.692%   $235.6506   $235.65   $235.65   $235.70  
  Purchase #3 $85.99   13.539%   $97.6322   $97.63   $97.65   $97.60  
  Purchase #4 $221.49   7.846%   $238.8681   $238.87   $238.85   $238.90  
  Purchase #5 $185.47   10.310%   $204.592   $204.59   $204.60   $204.60  
  Purchase #6 $84.25   11.829%   $94.2159   $94.22   $94.20   $94.20  
  Purchase #7 $147.84   3.218%   $152.5975   $152.60   $152.60   $152.60  
  7 purchase totals = $1,152.84       $1,247.5870   $1,247.59   $1,247.60   $1,247.60