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 $108.29   10.179%   $119.3128   $119.31   $119.30   $119.30  
  Purchase #2 $161.48   7.822%   $174.111   $174.11   $174.10   $174.10  
  Purchase #3 $85.82   6.213%   $91.152   $91.15   $91.15   $91.20  
  Purchase #4 $106.82   13.858%   $121.6231   $121.62   $121.60   $121.60  
  Purchase #5 $245.66   13.148%   $277.9594   $277.96   $277.95   $278.00  
  Purchase #6 $226.88   13.594%   $257.7221   $257.72   $257.70   $257.70  
  Purchase #7 $144.28   8.649%   $156.7588   $156.76   $156.75   $156.80  
  7 purchase totals = $1,079.23       $1,198.6392   $1,198.63   $1,198.55   $1,198.70