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 $132.98   12.468%   $149.5599   $149.56   $149.55   $149.60  
  Purchase #2 $120.81   13.874%   $137.5712   $137.57   $137.55   $137.60  
  Purchase #3 $179.85   13.814%   $204.6945   $204.69   $204.70   $204.70  
  Purchase #4 $242.43   6.839%   $259.0098   $259.01   $259.00   $259.00  
  Purchase #5 $187.65   6.397%   $199.654   $199.65   $199.65   $199.70  
  Purchase #6 $36.40   12.613%   $40.9911   $40.99   $41.00   $41.00  
  Purchase #7 $113.86   11.523%   $126.9801   $126.98   $127.00   $127.00  
  7 purchase totals = $1,013.98       $1,118.4606   $1,118.45   $1,118.45   $1,118.60