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 $62.36   13.274%   $70.6377   $70.64   $70.65   $70.60  
  Purchase #2 $218.76   4.308%   $228.1842   $228.18   $228.20   $228.20  
  Purchase #3 $189.34   6.140%   $200.9655   $200.97   $200.95   $201.00  
  Purchase #4 $197.37   11.466%   $220.0004   $220.00   $220.00   $220.00  
  Purchase #5 $82.84   4.104%   $86.2398   $86.24   $86.25   $86.20  
  Purchase #6 $210.36   5.254%   $221.4123   $221.41   $221.40   $221.40  
  Purchase #7 $121.78   3.303%   $125.8024   $125.80   $125.80   $125.80  
  7 purchase totals = $1,082.81       $1,153.2423   $1,153.24   $1,153.25   $1,153.20