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 $226.65   11.513%   $252.7442   $252.74   $252.75   $252.70  
  Purchase #2 $213.92   13.855%   $243.5586   $243.56   $243.55   $243.60  
  Purchase #3 $170.67   3.668%   $176.9302   $176.93   $176.95   $176.90  
  Purchase #4 $89.34   5.474%   $94.2305   $94.23   $94.25   $94.20  
  Purchase #5 $157.54   5.351%   $165.97   $165.97   $165.95   $166.00  
  Purchase #6 $232.32   9.386%   $254.1256   $254.13   $254.15   $254.10  
  Purchase #7 $87.40   10.359%   $96.4538   $96.45   $96.45   $96.50  
  7 purchase totals = $1,177.84       $1,284.0129   $1,284.01   $1,284.05   $1,284.00