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 $84.48   7.712%   $90.9951   $91.00   $91.00   $91.00  
  Purchase #2 $212.72   9.692%   $233.3368   $233.34   $233.35   $233.30  
  Purchase #3 $76.44   7.511%   $82.1814   $82.18   $82.20   $82.20  
  Purchase #4 $49.56   6.847%   $52.9534   $52.95   $52.95   $53.00  
  Purchase #5 $249.33   12.734%   $281.0797   $281.08   $281.10   $281.10  
  Purchase #6 $125.85   5.691%   $133.0121   $133.01   $133.00   $133.00  
  Purchase #7 $172.84   12.410%   $194.2894   $194.29   $194.30   $194.30  
  7 purchase totals = $971.22       $1,067.8479   $1,067.85   $1,067.90   $1,067.90