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 $60.61   4.675%   $63.4435   $63.44   $63.45   $63.40  
  Purchase #2 $171.39   11.822%   $191.6517   $191.65   $191.65   $191.70  
  Purchase #3 $149.68   5.316%   $157.637   $157.64   $157.65   $157.60  
  Purchase #4 $44.41   13.771%   $50.5257   $50.53   $50.55   $50.50  
  Purchase #5 $78.43   12.178%   $87.9812   $87.98   $88.00   $88.00  
  Purchase #6 $165.42   3.338%   $170.9417   $170.94   $170.95   $170.90  
  Purchase #7 $36.79   3.513%   $38.0824   $38.08   $38.10   $38.10  
  7 purchase totals = $706.73       $760.2632   $760.26   $760.35   $760.20