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 $210.60   7.697%   $226.8099   $226.81   $226.80   $226.80  
  Purchase #2 $127.67   8.205%   $138.1453   $138.15   $138.15   $138.10  
  Purchase #3 $46.94   8.344%   $50.8567   $50.86   $50.85   $50.90  
  Purchase #4 $212.33   5.243%   $223.4625   $223.46   $223.45   $223.50  
  Purchase #5 $237.38   9.484%   $259.8931   $259.89   $259.90   $259.90  
  Purchase #6 $188.58   4.191%   $196.4834   $196.48   $196.50   $196.50  
  Purchase #7 $69.54   7.751%   $74.93   $74.93   $74.95   $74.90  
  7 purchase totals = $1,093.04       $1,170.5809   $1,170.58   $1,170.60   $1,170.60