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 $124.53   7.631%   $134.0329   $134.03   $134.05   $134.00  
  Purchase #2 $106.46   11.267%   $118.4548   $118.45   $118.45   $118.50  
  Purchase #3 $209.39   5.814%   $221.5639   $221.56   $221.55   $221.60  
  Purchase #4 $237.98   11.295%   $264.8598   $264.86   $264.85   $264.90  
  Purchase #5 $232.87   4.155%   $242.5457   $242.55   $242.55   $242.50  
  Purchase #6 $90.61   8.191%   $98.0319   $98.03   $98.05   $98.00  
  Purchase #7 $113.54   6.337%   $120.735   $120.74   $120.75   $120.70  
  7 purchase totals = $1,115.38       $1,200.2240   $1,200.22   $1,200.25   $1,200.20