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 $53.45   8.730%   $58.1162   $58.12   $58.10   $58.10  
  Purchase #2 $88.66   5.269%   $93.3315   $93.33   $93.35   $93.30  
  Purchase #3 $75.73   13.304%   $85.8051   $85.81   $85.80   $85.80  
  Purchase #4 $194.62   4.576%   $203.5258   $203.53   $203.55   $203.50  
  Purchase #5 $229.91   6.513%   $244.884   $244.88   $244.90   $244.90  
  Purchase #6 $178.31   11.698%   $199.1687   $199.17   $199.15   $199.20  
  Purchase #7 $155.38   6.250%   $165.0913   $165.09   $165.10   $165.10  
  7 purchase totals = $976.06       $1,049.9226   $1,049.93   $1,049.95   $1,049.90