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 $92.25   4.636%   $96.5267   $96.53   $96.55   $96.50  
  Purchase #2 $80.39   9.392%   $87.9402   $87.94   $87.95   $87.90  
  Purchase #3 $218.28   13.441%   $247.619   $247.62   $247.60   $247.60  
  Purchase #4 $217.70   12.725%   $245.4023   $245.40   $245.40   $245.40  
  Purchase #5 $202.28   8.249%   $218.9661   $218.97   $218.95   $219.00  
  Purchase #6 $60.57   8.194%   $65.5331   $65.53   $65.55   $65.50  
  Purchase #7 $69.81   6.159%   $74.1096   $74.11   $74.10   $74.10  
  7 purchase totals = $941.28       $1,036.0970   $1,036.10   $1,036.10   $1,036.00