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 $174.59   5.248%   $183.7525   $183.75   $183.75   $183.80  
  Purchase #2 $89.93   7.124%   $96.3366   $96.34   $96.35   $96.30  
  Purchase #3 $120.90   5.234%   $127.2279   $127.23   $127.25   $127.20  
  Purchase #4 $106.55   4.809%   $111.674   $111.67   $111.65   $111.70  
  Purchase #5 $246.95   5.241%   $259.8926   $259.89   $259.90   $259.90  
  Purchase #6 $37.85   5.645%   $39.9866   $39.99   $40.00   $40.00  
  Purchase #7 $116.83   13.815%   $132.9701   $132.97   $132.95   $133.00  
  7 purchase totals = $893.60       $951.8403   $951.84   $951.85   $951.90