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 $85.33   9.580%   $93.5046   $93.50   $93.50   $93.50  
  Purchase #2 $241.29   3.343%   $249.3563   $249.36   $249.35   $249.40  
  Purchase #3 $39.51   3.833%   $41.0244   $41.02   $41.00   $41.00  
  Purchase #4 $190.39   13.577%   $216.2393   $216.24   $216.25   $216.20  
  Purchase #5 $104.83   4.547%   $109.5966   $109.60   $109.60   $109.60  
  Purchase #6 $203.96   5.363%   $214.8984   $214.90   $214.90   $214.90  
  Purchase #7 $149.79   12.220%   $168.0943   $168.09   $168.10   $168.10  
  7 purchase totals = $1,015.10       $1,092.7139   $1,092.71   $1,092.70   $1,092.70