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 $174.64   13.856%   $198.8381   $198.84   $198.85   $198.80  
  Purchase #2 $231.89   12.229%   $260.2478   $260.25   $260.25   $260.20  
  Purchase #3 $15.74   10.547%   $17.4001   $17.40   $17.40   $17.40  
  Purchase #4 $184.78   11.408%   $205.8597   $205.86   $205.85   $205.90  
  Purchase #5 $82.28   11.550%   $91.7833   $91.78   $91.80   $91.80  
  Purchase #6 $132.30   5.768%   $139.9311   $139.93   $139.95   $139.90  
  Purchase #7 $177.25   9.723%   $194.484   $194.48   $194.50   $194.50  
  7 purchase totals = $998.88       $1,108.5441   $1,108.54   $1,108.60   $1,108.50