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 $174.27   11.432%   $194.1925   $194.19   $194.20   $194.20  
  Purchase #2 $39.76   4.117%   $41.3969   $41.40   $41.40   $41.40  
  Purchase #3 $233.64   3.708%   $242.3034   $242.30   $242.30   $242.30  
  Purchase #4 $32.54   12.603%   $36.641   $36.64   $36.65   $36.60  
  Purchase #5 $151.72   5.511%   $160.0813   $160.08   $160.10   $160.10  
  Purchase #6 $59.56   4.470%   $62.2223   $62.22   $62.20   $62.20  
  Purchase #7 $38.40   6.216%   $40.7869   $40.79   $40.80   $40.80  
  7 purchase totals = $729.89       $777.6243   $777.62   $777.65   $777.60