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 $82.45   4.117%   $85.8445   $85.84   $85.85   $85.80  
  Purchase #2 $26.52   11.710%   $29.6255   $29.63   $29.65   $29.60  
  Purchase #3 $85.98   12.322%   $96.5745   $96.57   $96.55   $96.60  
  Purchase #4 $232.97   12.203%   $261.3993   $261.40   $261.40   $261.40  
  Purchase #5 $119.68   10.189%   $131.8742   $131.87   $131.85   $131.90  
  Purchase #6 $204.41   3.311%   $211.178   $211.18   $211.20   $211.20  
  Purchase #7 $171.63   5.826%   $181.6292   $181.63   $181.65   $181.60  
  7 purchase totals = $923.64       $998.1252   $998.12   $998.15   $998.10