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 $83.59   11.175%   $92.9312   $92.93   $92.95   $92.90  
  Purchase #2 $237.59   3.810%   $246.6422   $246.64   $246.65   $246.60  
  Purchase #3 $49.79   3.247%   $51.4067   $51.41   $51.40   $51.40  
  Purchase #4 $132.39   3.867%   $137.5095   $137.51   $137.50   $137.50  
  Purchase #5 $246.32   9.446%   $269.5874   $269.59   $269.60   $269.60  
  Purchase #6 $118.94   12.410%   $133.7005   $133.70   $133.70   $133.70  
  Purchase #7 $121.29   6.490%   $129.1617   $129.16   $129.15   $129.20  
  7 purchase totals = $989.91       $1,060.9392   $1,060.94   $1,060.95   $1,060.90