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 $234.46   4.822%   $245.7657   $245.77   $245.75   $245.80  
  Purchase #2 $228.78   13.529%   $259.7316   $259.73   $259.75   $259.70  
  Purchase #3 $169.56   6.404%   $180.4186   $180.42   $180.40   $180.40  
  Purchase #4 $219.66   6.308%   $233.5162   $233.52   $233.50   $233.50  
  Purchase #5 $76.29   5.638%   $80.5912   $80.59   $80.60   $80.60  
  Purchase #6 $200.50   4.106%   $208.7325   $208.73   $208.75   $208.70  
  Purchase #7 $191.81   10.433%   $211.8215   $211.82   $211.80   $211.80  
  7 purchase totals = $1,321.06       $1,420.5773   $1,420.58   $1,420.55   $1,420.50