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 $61.46   13.286%   $69.6256   $69.63   $69.65   $69.60  
  Purchase #2 $198.98   6.648%   $212.2082   $212.21   $212.20   $212.20  
  Purchase #3 $211.46   12.476%   $237.8417   $237.84   $237.85   $237.80  
  Purchase #4 $66.37   9.303%   $72.5444   $72.54   $72.55   $72.50  
  Purchase #5 $88.75   7.861%   $95.7266   $95.73   $95.75   $95.70  
  Purchase #6 $231.29   10.439%   $255.4344   $255.43   $255.45   $255.40  
  Purchase #7 $81.61   7.856%   $88.0213   $88.02   $88.00   $88.00  
  7 purchase totals = $939.92       $1,031.4022   $1,031.40   $1,031.45   $1,031.20