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 $153.51   8.491%   $166.5445   $166.54   $166.55   $166.50  
  Purchase #2 $54.43   8.292%   $58.9433   $58.94   $58.95   $58.90  
  Purchase #3 $194.26   4.803%   $203.5903   $203.59   $203.60   $203.60  
  Purchase #4 $89.45   8.400%   $96.9638   $96.96   $96.95   $97.00  
  Purchase #5 $162.79   5.627%   $171.9502   $171.95   $171.95   $172.00  
  Purchase #6 $163.98   6.406%   $174.4846   $174.48   $174.50   $174.50  
  Purchase #7 $210.55   7.467%   $226.2718   $226.27   $226.25   $226.30  
  7 purchase totals = $1,028.97       $1,098.7485   $1,098.73   $1,098.75   $1,098.80