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 $48.87   6.865%   $52.2249   $52.22   $52.20   $52.20  
  Purchase #2 $179.70   8.855%   $195.6124   $195.61   $195.60   $195.60  
  Purchase #3 $190.34   13.108%   $215.2898   $215.29   $215.30   $215.30  
  Purchase #4 $166.37   3.281%   $171.8286   $171.83   $171.85   $171.80  
  Purchase #5 $59.84   4.748%   $62.6812   $62.68   $62.70   $62.70  
  Purchase #6 $45.80   9.222%   $50.0237   $50.02   $50.00   $50.00  
  Purchase #7 $7.64   11.510%   $8.5194   $8.52   $8.50   $8.50  
  7 purchase totals = $698.56       $756.1800   $756.17   $756.15   $756.10