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 $245.37   8.793%   $266.9454   $266.95   $266.95   $266.90  
  Purchase #2 $116.68   4.516%   $121.9493   $121.95   $121.95   $121.90  
  Purchase #3 $159.52   3.839%   $165.644   $165.64   $165.65   $165.60  
  Purchase #4 $21.37   13.533%   $24.262   $24.26   $24.25   $24.30  
  Purchase #5 $23.52   7.636%   $25.316   $25.32   $25.30   $25.30  
  Purchase #6 $214.96   11.575%   $239.8416   $239.84   $239.85   $239.80  
  Purchase #7 $183.82   8.648%   $199.7168   $199.72   $199.70   $199.70  
  7 purchase totals = $965.24       $1,043.6751   $1,043.68   $1,043.65   $1,043.50