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 $225.75   12.562%   $254.1087   $254.11   $254.10   $254.10  
  Purchase #2 $93.94   9.581%   $102.9404   $102.94   $102.95   $102.90  
  Purchase #3 $90.46   13.477%   $102.6513   $102.65   $102.65   $102.70  
  Purchase #4 $236.35   9.851%   $259.6328   $259.63   $259.65   $259.60  
  Purchase #5 $241.39   13.542%   $274.079   $274.08   $274.10   $274.10  
  Purchase #6 $28.43   13.715%   $32.3292   $32.33   $32.35   $32.30  
  Purchase #7 $58.86   5.516%   $62.1067   $62.11   $62.10   $62.10  
  7 purchase totals = $975.18       $1,087.8481   $1,087.85   $1,087.90   $1,087.80