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 $120.56   5.475%   $127.1607   $127.16   $127.15   $127.20  
  Purchase #2 $8.26   6.865%   $8.827   $8.83   $8.85   $8.80  
  Purchase #3 $126.82   8.474%   $137.5667   $137.57   $137.55   $137.60  
  Purchase #4 $92.81   7.483%   $99.755   $99.76   $99.75   $99.80  
  Purchase #5 $241.44   10.360%   $266.4532   $266.45   $266.45   $266.50  
  Purchase #6 $180.35   5.179%   $189.6903   $189.69   $189.70   $189.70  
  Purchase #7 $225.34   9.501%   $246.7496   $246.75   $246.75   $246.70  
  7 purchase totals = $995.58       $1,076.2025   $1,076.21   $1,076.20   $1,076.30