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 $69.67   7.864%   $75.1488   $75.15   $75.15   $75.10  
  Purchase #2 $151.64   9.253%   $165.6712   $165.67   $165.65   $165.70  
  Purchase #3 $88.48   4.542%   $92.4988   $92.50   $92.50   $92.50  
  Purchase #4 $250.82   5.364%   $264.274   $264.27   $264.25   $264.30  
  Purchase #5 $207.49   13.163%   $234.8019   $234.80   $234.80   $234.80  
  Purchase #6 $101.53   12.203%   $113.9197   $113.92   $113.90   $113.90  
  Purchase #7 $141.64   4.496%   $148.0081   $148.01   $148.00   $148.00  
  7 purchase totals = $1,011.27       $1,094.3225   $1,094.32   $1,094.25   $1,094.30