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 $68.83   7.521%   $74.0067   $74.01   $74.00   $74.00  
  Purchase #2 $93.69   6.507%   $99.7864   $99.79   $99.80   $99.80  
  Purchase #3 $157.52   3.731%   $163.3971   $163.40   $163.40   $163.40  
  Purchase #4 $44.99   6.232%   $47.7938   $47.79   $47.80   $47.80  
  Purchase #5 $206.78   6.632%   $220.4936   $220.49   $220.50   $220.50  
  Purchase #6 $247.69   7.738%   $266.8563   $266.86   $266.85   $266.90  
  Purchase #7 $168.62   5.443%   $177.798   $177.80   $177.80   $177.80  
  7 purchase totals = $988.12       $1,050.1319   $1,050.14   $1,050.15   $1,050.20