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 $64.59   7.722%   $69.5776   $69.58   $69.60   $69.60  
  Purchase #2 $194.74   4.736%   $203.9629   $203.96   $203.95   $204.00  
  Purchase #3 $89.54   8.146%   $96.8339   $96.83   $96.85   $96.80  
  Purchase #4 $174.80   12.162%   $196.0592   $196.06   $196.05   $196.10  
  Purchase #5 $21.39   6.130%   $22.7012   $22.70   $22.70   $22.70  
  Purchase #6 $113.75   4.376%   $118.7277   $118.73   $118.75   $118.70  
  Purchase #7 $249.97   7.648%   $269.0877   $269.09   $269.10   $269.10  
  7 purchase totals = $908.78       $976.9502   $976.95   $977.00   $977.00