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 $66.29   6.757%   $70.7692   $70.77   $70.75   $70.80  
  Purchase #2 $113.97   5.546%   $120.2908   $120.29   $120.30   $120.30  
  Purchase #3 $118.69   11.310%   $132.1138   $132.11   $132.10   $132.10  
  Purchase #4 $214.54   11.396%   $238.989   $238.99   $239.00   $239.00  
  Purchase #5 $106.82   3.435%   $110.4893   $110.49   $110.50   $110.50  
  Purchase #6 $227.98   6.450%   $242.6847   $242.68   $242.70   $242.70  
  Purchase #7 $228.65   5.602%   $241.459   $241.46   $241.45   $241.50  
  7 purchase totals = $1,076.94       $1,156.7958   $1,156.79   $1,156.80   $1,156.90