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 $128.27   10.133%   $141.2676   $141.27   $141.25   $141.30  
  Purchase #2 $188.98   8.292%   $204.6502   $204.65   $204.65   $204.70  
  Purchase #3 $16.94   8.799%   $18.4306   $18.43   $18.45   $18.40  
  Purchase #4 $160.85   13.759%   $182.9814   $182.98   $183.00   $183.00  
  Purchase #5 $218.62   10.221%   $240.9652   $240.97   $240.95   $241.00  
  Purchase #6 $97.76   8.466%   $106.0364   $106.04   $106.05   $106.00  
  Purchase #7 $213.85   10.239%   $235.7461   $235.75   $235.75   $235.70  
  7 purchase totals = $1,025.27       $1,130.0775   $1,130.09   $1,130.10   $1,130.10