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 $97.63   3.513%   $101.0597   $101.06   $101.05   $101.10  
  Purchase #2 $197.67   5.666%   $208.87   $208.87   $208.85   $208.90  
  Purchase #3 $215.61   12.826%   $243.2641   $243.26   $243.25   $243.30  
  Purchase #4 $71.94   3.809%   $74.6802   $74.68   $74.70   $74.70  
  Purchase #5 $63.52   3.751%   $65.9026   $65.90   $65.90   $65.90  
  Purchase #6 $103.65   8.852%   $112.8251   $112.83   $112.85   $112.80  
  Purchase #7 $84.71   3.218%   $87.436   $87.44   $87.45   $87.40  
  7 purchase totals = $834.73       $894.0377   $894.04   $894.05   $894.10