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 $47.27   11.537%   $52.7235   $52.72   $52.70   $52.70  
  Purchase #2 $250.59   8.477%   $271.8325   $271.83   $271.85   $271.80  
  Purchase #3 $103.68   5.151%   $109.0206   $109.02   $109.00   $109.00  
  Purchase #4 $200.58   5.518%   $211.648   $211.65   $211.65   $211.60  
  Purchase #5 $208.25   7.750%   $224.3894   $224.39   $224.40   $224.40  
  Purchase #6 $49.79   4.154%   $51.8583   $51.86   $51.85   $51.90  
  Purchase #7 $232.93   9.231%   $254.4318   $254.43   $254.45   $254.40  
  7 purchase totals = $1,093.09       $1,175.9041   $1,175.90   $1,175.90   $1,175.80