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 $205.87   9.236%   $224.8842   $224.88   $224.90   $224.90  
  Purchase #2 $110.48   13.161%   $125.0203   $125.02   $125.00   $125.00  
  Purchase #3 $52.89   9.448%   $57.887   $57.89   $57.90   $57.90  
  Purchase #4 $67.43   10.378%   $74.4279   $74.43   $74.45   $74.40  
  Purchase #5 $228.50   13.512%   $259.3749   $259.37   $259.35   $259.40  
  Purchase #6 $17.97   13.243%   $20.3498   $20.35   $20.35   $20.30  
  Purchase #7 $235.47   12.490%   $264.8802   $264.88   $264.90   $264.90  
  7 purchase totals = $918.61       $1,026.8243   $1,026.82   $1,026.85   $1,026.80