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 $161.67   3.626%   $167.5322   $167.53   $167.55   $167.50  
  Purchase #2 $130.68   10.168%   $143.9675   $143.97   $143.95   $144.00  
  Purchase #3 $12.46   4.778%   $13.0553   $13.06   $13.05   $13.10  
  Purchase #4 $35.41   10.696%   $39.1975   $39.20   $39.20   $39.20  
  Purchase #5 $159.65   3.534%   $165.292   $165.29   $165.30   $165.30  
  Purchase #6 $212.29   4.796%   $222.4714   $222.47   $222.45   $222.50  
  Purchase #7 $232.61   13.350%   $263.6634   $263.66   $263.65   $263.70  
  7 purchase totals = $944.77       $1,015.1793   $1,015.18   $1,015.15   $1,015.30