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 $96.52   5.112%   $101.4541   $101.45   $101.45   $101.50  
  Purchase #2 $24.46   4.696%   $25.6086   $25.61   $25.60   $25.60  
  Purchase #3 $45.25   7.530%   $48.6573   $48.66   $48.65   $48.70  
  Purchase #4 $191.97   5.568%   $202.6589   $202.66   $202.65   $202.70  
  Purchase #5 $121.62   11.693%   $135.841   $135.84   $135.85   $135.80  
  Purchase #6 $197.48   13.707%   $224.5486   $224.55   $224.55   $224.50  
  Purchase #7 $95.82   13.235%   $108.5018   $108.50   $108.50   $108.50  
  7 purchase totals = $773.12       $847.2703   $847.27   $847.25   $847.30