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 $88.81   5.301%   $93.5178   $93.52   $93.50   $93.50  
  Purchase #2 $218.96   6.774%   $233.7924   $233.79   $233.80   $233.80  
  Purchase #3 $109.88   7.586%   $118.2155   $118.22   $118.20   $118.20  
  Purchase #4 $113.40   4.556%   $118.5665   $118.57   $118.55   $118.60  
  Purchase #5 $138.29   9.439%   $151.3432   $151.34   $151.35   $151.30  
  Purchase #6 $101.68   4.605%   $106.3624   $106.36   $106.35   $106.40  
  Purchase #7 $42.63   11.113%   $47.3675   $47.37   $47.35   $47.40  
  7 purchase totals = $813.65       $869.1653   $869.17   $869.10   $869.20