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 $125.64   4.696%   $131.5401   $131.54   $131.55   $131.50  
  Purchase #2 $216.64   13.415%   $245.7023   $245.70   $245.70   $245.70  
  Purchase #3 $214.87   9.821%   $235.9724   $235.97   $235.95   $236.00  
  Purchase #4 $170.36   10.151%   $187.6532   $187.65   $187.65   $187.70  
  Purchase #5 $53.56   13.184%   $60.6214   $60.62   $60.60   $60.60  
  Purchase #6 $87.50   6.743%   $93.4001   $93.40   $93.40   $93.40  
  Purchase #7 $38.45   3.170%   $39.6689   $39.67   $39.65   $39.70  
  7 purchase totals = $907.02       $994.5584   $994.55   $994.50   $994.60