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 $91.94   12.418%   $103.3571   $103.36   $103.35   $103.40  
  Purchase #2 $202.64   10.363%   $223.6396   $223.64   $223.65   $223.60  
  Purchase #3 $111.69   8.440%   $121.1166   $121.12   $121.10   $121.10  
  Purchase #4 $98.83   3.643%   $102.4304   $102.43   $102.45   $102.40  
  Purchase #5 $131.60   6.824%   $140.5804   $140.58   $140.60   $140.60  
  Purchase #6 $71.86   7.817%   $77.4773   $77.48   $77.50   $77.50  
  Purchase #7 $224.96   9.476%   $246.2772   $246.28   $246.30   $246.30  
  7 purchase totals = $933.52       $1,014.8786   $1,014.89   $1,014.95   $1,014.90