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 $194.78   10.264%   $214.7722   $214.77   $214.75   $214.80  
  Purchase #2 $138.54   9.497%   $151.6971   $151.70   $151.70   $151.70  
  Purchase #3 $214.49   7.320%   $230.1907   $230.19   $230.20   $230.20  
  Purchase #4 $98.84   8.791%   $107.529   $107.53   $107.55   $107.50  
  Purchase #5 $144.46   3.667%   $149.7573   $149.76   $149.75   $149.80  
  Purchase #6 $24.37   11.213%   $27.1026   $27.10   $27.10   $27.10  
  Purchase #7 $165.47   9.188%   $180.6734   $180.67   $180.65   $180.70  
  7 purchase totals = $980.95       $1,061.7223   $1,061.72   $1,061.70   $1,061.80