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 $114.28   6.120%   $121.2739   $121.27   $121.25   $121.30  
  Purchase #2 $56.79   7.310%   $60.9413   $60.94   $60.95   $60.90  
  Purchase #3 $111.33   7.275%   $119.4293   $119.43   $119.45   $119.40  
  Purchase #4 $120.39   8.165%   $130.2198   $130.22   $130.20   $130.20  
  Purchase #5 $184.37   6.123%   $195.659   $195.66   $195.65   $195.70  
  Purchase #6 $132.84   5.837%   $140.5939   $140.59   $140.60   $140.60  
  Purchase #7 $17.83   6.250%   $18.9444   $18.94   $18.95   $18.90  
  7 purchase totals = $737.83       $787.0616   $787.05   $787.05   $787.00