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 $112.84   5.662%   $119.229   $119.23   $119.25   $119.20  
  Purchase #2 $157.94   12.603%   $177.8452   $177.85   $177.85   $177.80  
  Purchase #3 $136.48   6.367%   $145.1697   $145.17   $145.15   $145.20  
  Purchase #4 $51.70   10.120%   $56.932   $56.93   $56.95   $56.90  
  Purchase #5 $135.71   13.144%   $153.5477   $153.55   $153.55   $153.50  
  Purchase #6 $43.43   11.412%   $48.3862   $48.39   $48.40   $48.40  
  Purchase #7 $48.61   12.264%   $54.5715   $54.57   $54.55   $54.60  
  7 purchase totals = $686.71       $755.6813   $755.69   $755.70   $755.60