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 $68.39   13.223%   $77.4332   $77.43   $77.45   $77.40  
  Purchase #2 $50.54   11.652%   $56.4289   $56.43   $56.45   $56.40  
  Purchase #3 $228.47   5.748%   $241.6025   $241.60   $241.60   $241.60  
  Purchase #4 $187.39   8.228%   $202.8084   $202.81   $202.80   $202.80  
  Purchase #5 $163.70   3.375%   $169.2249   $169.22   $169.20   $169.20  
  Purchase #6 $136.85   4.195%   $142.5909   $142.59   $142.60   $142.60  
  Purchase #7 $246.51   3.433%   $254.9727   $254.97   $254.95   $255.00  
  7 purchase totals = $1,081.85       $1,145.0615   $1,145.05   $1,145.05   $1,145.00