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 $228.44   5.704%   $241.4702   $241.47   $241.45   $241.50  
  Purchase #2 $108.76   4.764%   $113.9413   $113.94   $113.95   $113.90  
  Purchase #3 $211.87   6.493%   $225.6267   $225.63   $225.65   $225.60  
  Purchase #4 $54.53   8.860%   $59.3614   $59.36   $59.35   $59.40  
  Purchase #5 $183.27   10.678%   $202.8396   $202.84   $202.85   $202.80  
  Purchase #6 $232.75   7.598%   $250.4343   $250.43   $250.45   $250.40  
  Purchase #7 $6.80   7.413%   $7.3041   $7.30   $7.30   $7.30  
  7 purchase totals = $1,026.42       $1,100.9776   $1,100.97   $1,101.00   $1,100.90