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 $65.93   3.180%   $68.0266   $68.03   $68.05   $68.00  
  Purchase #2 $99.46   10.263%   $109.6676   $109.67   $109.65   $109.70  
  Purchase #3 $155.30   7.123%   $166.362   $166.36   $166.35   $166.40  
  Purchase #4 $75.70   5.855%   $80.1322   $80.13   $80.15   $80.10  
  Purchase #5 $35.43   10.260%   $39.0651   $39.07   $39.05   $39.10  
  Purchase #6 $75.83   11.427%   $84.4951   $84.50   $84.50   $84.50  
  Purchase #7 $242.28   5.773%   $256.2668   $256.27   $256.25   $256.30  
  7 purchase totals = $749.93       $804.0154   $804.03   $804.00   $804.10