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 $212.67   6.524%   $226.5446   $226.54   $226.55   $226.50  
  Purchase #2 $213.80   8.841%   $232.7021   $232.70   $232.70   $232.70  
  Purchase #3 $83.49   11.344%   $92.9611   $92.96   $92.95   $93.00  
  Purchase #4 $149.73   10.388%   $165.284   $165.28   $165.30   $165.30  
  Purchase #5 $215.62   12.425%   $242.4108   $242.41   $242.40   $242.40  
  Purchase #6 $81.69   12.592%   $91.9764   $91.98   $92.00   $92.00  
  Purchase #7 $26.99   3.766%   $28.0064   $28.01   $28.00   $28.00  
  7 purchase totals = $983.99       $1,079.8854   $1,079.88   $1,079.90   $1,079.90