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 $250.67   5.532%   $264.5371   $264.54   $264.55   $264.50  
  Purchase #2 $121.34   4.642%   $126.9726   $126.97   $126.95   $127.00  
  Purchase #3 $175.84   4.365%   $183.5154   $183.52   $183.50   $183.50  
  Purchase #4 $151.84   5.123%   $159.6188   $159.62   $159.60   $159.60  
  Purchase #5 $153.69   3.834%   $159.5825   $159.58   $159.60   $159.60  
  Purchase #6 $83.94   12.784%   $94.6709   $94.67   $94.65   $94.70  
  Purchase #7 $215.89   3.847%   $224.1953   $224.20   $224.20   $224.20  
  7 purchase totals = $1,153.21       $1,213.0926   $1,213.10   $1,213.05   $1,213.10