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 $207.65   11.539%   $231.6107   $231.61   $231.60   $231.60  
  Purchase #2 $48.66   8.819%   $52.9513   $52.95   $52.95   $53.00  
  Purchase #3 $194.95   9.103%   $212.6963   $212.70   $212.70   $212.70  
  Purchase #4 $197.66   12.320%   $222.0117   $222.01   $222.00   $222.00  
  Purchase #5 $197.72   10.456%   $218.3936   $218.39   $218.40   $218.40  
  Purchase #6 $212.37   13.752%   $241.5751   $241.58   $241.60   $241.60  
  Purchase #7 $18.47   13.300%   $20.9265   $20.93   $20.95   $20.90  
  7 purchase totals = $1,077.48       $1,200.1652   $1,200.17   $1,200.20   $1,200.20