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 $58.61   13.563%   $66.5593   $66.56   $66.55   $66.60  
  Purchase #2 $236.37   7.536%   $254.1828   $254.18   $254.20   $254.20  
  Purchase #3 $143.59   4.841%   $150.5412   $150.54   $150.55   $150.50  
  Purchase #4 $218.50   10.740%   $241.9669   $241.97   $241.95   $242.00  
  Purchase #5 $134.97   4.777%   $141.4175   $141.42   $141.40   $141.40  
  Purchase #6 $29.37   7.372%   $31.5352   $31.54   $31.55   $31.50  
  Purchase #7 $126.34   8.201%   $136.7011   $136.70   $136.70   $136.70  
  7 purchase totals = $947.75       $1,022.9040   $1,022.91   $1,022.90   $1,022.90