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 $158.66   9.643%   $173.9596   $173.96   $173.95   $174.00  
  Purchase #2 $146.85   13.515%   $166.6968   $166.70   $166.70   $166.70  
  Purchase #3 $25.33   7.713%   $27.2837   $27.28   $27.30   $27.30  
  Purchase #4 $173.94   4.463%   $181.7029   $181.70   $181.70   $181.70  
  Purchase #5 $156.88   11.393%   $174.7533   $174.75   $174.75   $174.80  
  Purchase #6 $135.96   3.398%   $140.5799   $140.58   $140.60   $140.60  
  Purchase #7 $154.93   10.820%   $171.6934   $171.69   $171.70   $171.70  
  7 purchase totals = $952.55       $1,036.6696   $1,036.66   $1,036.70   $1,036.80