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 $239.73   11.392%   $267.04   $267.04   $267.05   $267.00  
  Purchase #2 $229.48   9.550%   $251.3953   $251.40   $251.40   $251.40  
  Purchase #3 $239.77   8.586%   $260.3567   $260.36   $260.35   $260.40  
  Purchase #4 $124.61   8.649%   $135.3875   $135.39   $135.40   $135.40  
  Purchase #5 $57.85   11.335%   $64.4073   $64.41   $64.40   $64.40  
  Purchase #6 $39.95   7.689%   $43.0218   $43.02   $43.00   $43.00  
  Purchase #7 $167.40   12.419%   $188.1894   $188.19   $188.20   $188.20  
  7 purchase totals = $1,098.79       $1,209.7980   $1,209.81   $1,209.80   $1,209.80