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 $174.25   10.558%   $192.6473   $192.65   $192.65   $192.60  
  Purchase #2 $65.78   3.565%   $68.1251   $68.13   $68.15   $68.10  
  Purchase #3 $77.57   7.394%   $83.3055   $83.31   $83.30   $83.30  
  Purchase #4 $67.48   5.285%   $71.0463   $71.05   $71.05   $71.00  
  Purchase #5 $246.99   12.557%   $278.0045   $278.00   $278.00   $278.00  
  Purchase #6 $234.84   5.265%   $247.2043   $247.20   $247.20   $247.20  
  Purchase #7 $106.68   12.825%   $120.3617   $120.36   $120.35   $120.40  
  7 purchase totals = $973.59       $1,060.6947   $1,060.70   $1,060.70   $1,060.60