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 $183.57   11.297%   $204.3079   $204.31   $204.30   $204.30  
  Purchase #2 $158.70   4.513%   $165.8621   $165.86   $165.85   $165.90  
  Purchase #3 $85.90   7.133%   $92.0272   $92.03   $92.05   $92.00  
  Purchase #4 $62.40   12.828%   $70.4047   $70.40   $70.40   $70.40  
  Purchase #5 $173.49   6.230%   $184.2984   $184.30   $184.30   $184.30  
  Purchase #6 $113.39   9.515%   $124.1791   $124.18   $124.20   $124.20  
  Purchase #7 $212.47   5.844%   $224.8867   $224.89   $224.90   $224.90  
  7 purchase totals = $989.92       $1,065.9661   $1,065.97   $1,066.00   $1,066.00