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 $134.75   8.818%   $146.6323   $146.63   $146.65   $146.60  
  Purchase #2 $106.89   11.855%   $119.5618   $119.56   $119.55   $119.60  
  Purchase #3 $219.90   8.740%   $239.1193   $239.12   $239.10   $239.10  
  Purchase #4 $85.35   9.588%   $93.5334   $93.53   $93.55   $93.50  
  Purchase #5 $110.39   3.567%   $114.3276   $114.33   $114.35   $114.30  
  Purchase #6 $241.51   5.521%   $254.8438   $254.84   $254.85   $254.80  
  Purchase #7 $171.30   12.444%   $192.6166   $192.62   $192.60   $192.60  
  7 purchase totals = $1,070.09       $1,160.6348   $1,160.63   $1,160.65   $1,160.50