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 $248.92   13.658%   $282.9175   $282.92   $282.90   $282.90  
  Purchase #2 $207.82   13.712%   $236.3163   $236.32   $236.30   $236.30  
  Purchase #3 $155.41   10.200%   $171.2618   $171.26   $171.25   $171.30  
  Purchase #4 $124.52   6.432%   $132.5291   $132.53   $132.55   $132.50  
  Purchase #5 $179.65   6.361%   $191.0775   $191.08   $191.10   $191.10  
  Purchase #6 $137.49   9.703%   $150.8307   $150.83   $150.85   $150.80  
  Purchase #7 $56.86   6.797%   $60.7248   $60.72   $60.70   $60.70  
  7 purchase totals = $1,110.67       $1,225.6577   $1,225.66   $1,225.65   $1,225.60