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 $58.41   3.209%   $60.2844   $60.28   $60.30   $60.30  
  Purchase #2 $99.84   6.839%   $106.6681   $106.67   $106.65   $106.70  
  Purchase #3 $139.78   4.484%   $146.0477   $146.05   $146.05   $146.00  
  Purchase #4 $39.59   10.373%   $43.6967   $43.70   $43.70   $43.70  
  Purchase #5 $241.33   11.713%   $269.597   $269.60   $269.60   $269.60  
  Purchase #6 $152.60   6.249%   $162.136   $162.14   $162.15   $162.10  
  Purchase #7 $222.86   9.738%   $244.5621   $244.56   $244.55   $244.60  
  7 purchase totals = $954.41       $1,032.9920   $1,033.00   $1,033.00   $1,033.00