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 $151.82   5.404%   $160.0244   $160.02   $160.00   $160.00  
  Purchase #2 $86.28   10.572%   $95.4015   $95.40   $95.40   $95.40  
  Purchase #3 $141.32   9.353%   $154.5377   $154.54   $154.55   $154.50  
  Purchase #4 $110.32   7.465%   $118.5554   $118.56   $118.55   $118.60  
  Purchase #5 $195.30   4.409%   $203.9108   $203.91   $203.90   $203.90  
  Purchase #6 $156.91   6.251%   $166.7184   $166.72   $166.70   $166.70  
  Purchase #7 $202.58   12.647%   $228.2003   $228.20   $228.20   $228.20  
  7 purchase totals = $1,044.53       $1,127.3485   $1,127.35   $1,127.30   $1,127.30