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 $164.79   13.452%   $186.9576   $186.96   $186.95   $187.00  
  Purchase #2 $29.50   11.195%   $32.8025   $32.80   $32.80   $32.80  
  Purchase #3 $9.58   5.849%   $10.1403   $10.14   $10.15   $10.10  
  Purchase #4 $226.29   10.459%   $249.9577   $249.96   $249.95   $250.00  
  Purchase #5 $162.32   6.710%   $173.2117   $173.21   $173.20   $173.20  
  Purchase #6 $213.76   5.631%   $225.7968   $225.80   $225.80   $225.80  
  Purchase #7 $188.90   7.794%   $203.6229   $203.62   $203.60   $203.60  
  7 purchase totals = $995.14       $1,082.4895   $1,082.49   $1,082.45   $1,082.50