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 $228.98   10.749%   $253.5931   $253.59   $253.60   $253.60  
  Purchase #2 $26.88   5.794%   $28.4374   $28.44   $28.45   $28.40  
  Purchase #3 $67.32   12.322%   $75.6152   $75.62   $75.60   $75.60  
  Purchase #4 $74.88   6.604%   $79.8251   $79.83   $79.85   $79.80  
  Purchase #5 $102.97   13.286%   $116.6506   $116.65   $116.65   $116.70  
  Purchase #6 $232.26   9.483%   $254.2852   $254.29   $254.30   $254.30  
  Purchase #7 $230.65   11.530%   $257.2439   $257.24   $257.25   $257.20  
  7 purchase totals = $963.94       $1,065.6505   $1,065.66   $1,065.70   $1,065.60