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 $54.45   12.245%   $61.1174   $61.12   $61.10   $61.10  
  Purchase #2 $64.57   10.770%   $71.5242   $71.52   $71.50   $71.50  
  Purchase #3 $119.96   3.411%   $124.0518   $124.05   $124.05   $124.10  
  Purchase #4 $180.29   8.722%   $196.0149   $196.01   $196.00   $196.00  
  Purchase #5 $103.37   4.460%   $107.9803   $107.98   $108.00   $108.00  
  Purchase #6 $128.67   5.666%   $135.9604   $135.96   $135.95   $136.00  
  Purchase #7 $248.71   7.440%   $267.214   $267.21   $267.20   $267.20  
  7 purchase totals = $900.02       $963.8630   $963.85   $963.80   $963.90