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 $211.48   11.343%   $235.4682   $235.47   $235.45   $235.50  
  Purchase #2 $168.68   10.616%   $186.5871   $186.59   $186.60   $186.60  
  Purchase #3 $208.62   9.455%   $228.345   $228.35   $228.35   $228.30  
  Purchase #4 $87.30   9.327%   $95.4425   $95.44   $95.45   $95.40  
  Purchase #5 $223.30   4.625%   $233.6276   $233.63   $233.65   $233.60  
  Purchase #6 $188.57   3.352%   $194.8909   $194.89   $194.90   $194.90  
  Purchase #7 $182.60   9.771%   $200.4418   $200.44   $200.45   $200.40  
  7 purchase totals = $1,270.55       $1,374.8031   $1,374.81   $1,374.85   $1,374.70