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 $83.35   12.221%   $93.5362   $93.54   $93.55   $93.50  
  Purchase #2 $180.87   11.297%   $201.3029   $201.30   $201.30   $201.30  
  Purchase #3 $84.38   7.108%   $90.3777   $90.38   $90.40   $90.40  
  Purchase #4 $151.83   12.645%   $171.0289   $171.03   $171.05   $171.00  
  Purchase #5 $179.44   8.482%   $194.6601   $194.66   $194.65   $194.70  
  Purchase #6 $221.38   10.649%   $244.9548   $244.95   $244.95   $245.00  
  Purchase #7 $73.68   9.852%   $80.939   $80.94   $80.95   $80.90  
  7 purchase totals = $974.93       $1,076.7996   $1,076.80   $1,076.85   $1,076.80