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 $184.87   10.139%   $203.614   $203.61   $203.60   $203.60  
  Purchase #2 $74.30   4.417%   $77.5818   $77.58   $77.60   $77.60  
  Purchase #3 $42.96   11.314%   $47.8205   $47.82   $47.80   $47.80  
  Purchase #4 $183.29   10.724%   $202.946   $202.95   $202.95   $202.90  
  Purchase #5 $151.40   10.204%   $166.8489   $166.85   $166.85   $166.80  
  Purchase #6 $240.84   12.257%   $270.3598   $270.36   $270.35   $270.40  
  Purchase #7 $194.81   7.323%   $209.0759   $209.08   $209.10   $209.10  
  7 purchase totals = $1,072.47       $1,178.2469   $1,178.25   $1,178.25   $1,178.20