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 $78.36   6.512%   $83.4628   $83.46   $83.45   $83.50  
  Purchase #2 $10.97   6.340%   $11.6655   $11.67   $11.65   $11.70  
  Purchase #3 $124.33   3.690%   $128.9178   $128.92   $128.90   $128.90  
  Purchase #4 $84.35   11.526%   $94.0722   $94.07   $94.05   $94.10  
  Purchase #5 $61.96   3.641%   $64.216   $64.22   $64.20   $64.20  
  Purchase #6 $204.38   10.617%   $226.079   $226.08   $226.10   $226.10  
  Purchase #7 $38.45   13.801%   $43.7565   $43.76   $43.75   $43.80  
  7 purchase totals = $602.80       $652.1698   $652.18   $652.10   $652.30