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 $184.39   9.130%   $201.2248   $201.22   $201.20   $201.20  
  Purchase #2 $32.84   10.525%   $36.2964   $36.30   $36.30   $36.30  
  Purchase #3 $22.95   11.655%   $25.6248   $25.62   $25.60   $25.60  
  Purchase #4 $195.54   5.615%   $206.5196   $206.52   $206.50   $206.50  
  Purchase #5 $51.38   4.266%   $53.5719   $53.57   $53.55   $53.60  
  Purchase #6 $235.61   3.110%   $242.9375   $242.94   $242.95   $242.90  
  Purchase #7 $219.25   12.462%   $246.5729   $246.57   $246.55   $246.60  
  7 purchase totals = $941.96       $1,012.7479   $1,012.74   $1,012.65   $1,012.70