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 $161.85   5.242%   $170.3342   $170.33   $170.35   $170.30  
  Purchase #2 $235.31   3.453%   $243.4353   $243.44   $243.45   $243.40  
  Purchase #3 $30.25   4.777%   $31.695   $31.70   $31.70   $31.70  
  Purchase #4 $46.27   11.511%   $51.5961   $51.60   $51.60   $51.60  
  Purchase #5 $165.61   5.577%   $174.8461   $174.85   $174.85   $174.80  
  Purchase #6 $83.46   11.855%   $93.3542   $93.35   $93.35   $93.40  
  Purchase #7 $98.33   4.728%   $102.979   $102.98   $103.00   $103.00  
  7 purchase totals = $821.08       $868.2399   $868.25   $868.30   $868.20