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 $126.99   3.434%   $131.3508   $131.35   $131.35   $131.40  
  Purchase #2 $183.84   11.421%   $204.8364   $204.84   $204.85   $204.80  
  Purchase #3 $240.41   11.465%   $267.973   $267.97   $267.95   $268.00  
  Purchase #4 $208.40   8.624%   $226.3724   $226.37   $226.35   $226.40  
  Purchase #5 $67.66   4.840%   $70.9347   $70.93   $70.95   $70.90  
  Purchase #6 $13.95   11.212%   $15.5141   $15.51   $15.50   $15.50  
  Purchase #7 $141.80   5.508%   $149.6103   $149.61   $149.60   $149.60  
  7 purchase totals = $983.05       $1,066.5917   $1,066.58   $1,066.55   $1,066.60