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 $53.61   12.282%   $60.1944   $60.19   $60.20   $60.20  
  Purchase #2 $74.54   3.666%   $77.2726   $77.27   $77.25   $77.30  
  Purchase #3 $85.40   12.357%   $95.9529   $95.95   $95.95   $96.00  
  Purchase #4 $212.63   6.258%   $225.9364   $225.94   $225.95   $225.90  
  Purchase #5 $71.27   12.757%   $80.3619   $80.36   $80.35   $80.40  
  Purchase #6 $231.81   9.809%   $254.5482   $254.55   $254.55   $254.50  
  Purchase #7 $244.37   10.660%   $270.4198   $270.42   $270.40   $270.40  
  7 purchase totals = $973.63       $1,064.6862   $1,064.68   $1,064.65   $1,064.70