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 $168.42   13.777%   $191.6232   $191.62   $191.60   $191.60  
  Purchase #2 $241.84   7.173%   $259.1872   $259.19   $259.20   $259.20  
  Purchase #3 $209.49   3.602%   $217.0358   $217.04   $217.05   $217.00  
  Purchase #4 $246.53   12.424%   $277.1589   $277.16   $277.15   $277.20  
  Purchase #5 $45.55   6.169%   $48.36   $48.36   $48.35   $48.40  
  Purchase #6 $166.80   8.523%   $181.0164   $181.02   $181.00   $181.00  
  Purchase #7 $53.56   12.772%   $60.4007   $60.40   $60.40   $60.40  
  7 purchase totals = $1,132.19       $1,234.7822   $1,234.79   $1,234.75   $1,234.80