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 $231.59   6.674%   $247.0463   $247.05   $247.05   $247.00  
  Purchase #2 $180.62   12.305%   $202.8453   $202.85   $202.85   $202.80  
  Purchase #3 $179.49   3.732%   $186.1886   $186.19   $186.20   $186.20  
  Purchase #4 $165.93   10.868%   $183.9633   $183.96   $183.95   $184.00  
  Purchase #5 $85.91   6.141%   $91.1857   $91.19   $91.20   $91.20  
  Purchase #6 $237.89   6.181%   $252.594   $252.59   $252.60   $252.60  
  Purchase #7 $234.53   12.641%   $264.1769   $264.18   $264.20   $264.20  
  7 purchase totals = $1,315.96       $1,428.0001   $1,428.01   $1,428.05   $1,428.00