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 $201.65   8.203%   $218.1913   $218.19   $218.20   $218.20  
  Purchase #2 $126.45   7.576%   $136.0299   $136.03   $136.05   $136.00  
  Purchase #3 $43.26   11.862%   $48.3915   $48.39   $48.40   $48.40  
  Purchase #4 $123.29   5.739%   $130.3656   $130.37   $130.35   $130.40  
  Purchase #5 $192.34   9.791%   $211.172   $211.17   $211.15   $211.20  
  Purchase #6 $237.87   5.168%   $250.1631   $250.16   $250.15   $250.20  
  Purchase #7 $216.34   3.538%   $223.9941   $223.99   $224.00   $224.00  
  7 purchase totals = $1,141.20       $1,218.3075   $1,218.30   $1,218.30   $1,218.40