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 $98.66   3.398%   $102.0125   $102.01   $102.00   $102.00  
  Purchase #2 $162.56   5.710%   $171.8422   $171.84   $171.85   $171.80  
  Purchase #3 $147.32   4.251%   $153.5826   $153.58   $153.60   $153.60  
  Purchase #4 $59.65   6.562%   $63.5642   $63.56   $63.55   $63.60  
  Purchase #5 $213.75   12.120%   $239.6565   $239.66   $239.65   $239.70  
  Purchase #6 $100.42   13.187%   $113.6624   $113.66   $113.65   $113.70  
  Purchase #7 $53.70   13.777%   $61.0982   $61.10   $61.10   $61.10  
  7 purchase totals = $836.06       $905.4186   $905.41   $905.40   $905.50