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 $219.26   12.426%   $246.5052   $246.51   $246.50   $246.50  
  Purchase #2 $204.30   12.624%   $230.0908   $230.09   $230.10   $230.10  
  Purchase #3 $125.64   10.504%   $138.8372   $138.84   $138.85   $138.80  
  Purchase #4 $102.30   7.155%   $109.6196   $109.62   $109.60   $109.60  
  Purchase #5 $243.92   7.492%   $262.1945   $262.19   $262.20   $262.20  
  Purchase #6 $29.53   13.702%   $33.5762   $33.58   $33.60   $33.60  
  Purchase #7 $11.27   3.138%   $11.6237   $11.62   $11.60   $11.60  
  7 purchase totals = $936.22       $1,032.4472   $1,032.45   $1,032.45   $1,032.40