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 $152.29   5.484%   $160.6416   $160.64   $160.65   $160.60  
  Purchase #2 $73.90   10.557%   $81.7016   $81.70   $81.70   $81.70  
  Purchase #3 $143.88   3.344%   $148.6913   $148.69   $148.70   $148.70  
  Purchase #4 $145.98   13.544%   $165.7515   $165.75   $165.75   $165.80  
  Purchase #5 $90.91   13.624%   $103.2956   $103.30   $103.30   $103.30  
  Purchase #6 $5.80   11.379%   $6.46   $6.46   $6.45   $6.50  
  Purchase #7 $34.42   4.187%   $35.8612   $35.86   $35.85   $35.90  
  7 purchase totals = $647.18       $702.4028   $702.40   $702.40   $702.50