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 $76.27   4.192%   $79.4672   $79.47   $79.45   $79.50  
  Purchase #2 $206.59   3.756%   $214.3495   $214.35   $214.35   $214.30  
  Purchase #3 $112.64   10.650%   $124.6362   $124.64   $124.65   $124.60  
  Purchase #4 $133.56   9.702%   $146.518   $146.52   $146.50   $146.50  
  Purchase #5 $156.50   4.669%   $163.807   $163.81   $163.80   $163.80  
  Purchase #6 $171.70   9.306%   $187.6784   $187.68   $187.70   $187.70  
  Purchase #7 $197.34   3.655%   $204.5528   $204.55   $204.55   $204.60  
  7 purchase totals = $1,054.60       $1,121.0091   $1,121.02   $1,121.00   $1,121.00