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 $83.30   11.488%   $92.8695   $92.87   $92.85   $92.90  
  Purchase #2 $222.32   9.651%   $243.7761   $243.78   $243.80   $243.80  
  Purchase #3 $156.97   9.829%   $172.3986   $172.40   $172.40   $172.40  
  Purchase #4 $145.25   8.583%   $157.7168   $157.72   $157.70   $157.70  
  Purchase #5 $226.85   6.635%   $241.9015   $241.90   $241.90   $241.90  
  Purchase #6 $14.65   9.711%   $16.0727   $16.07   $16.05   $16.10  
  Purchase #7 $172.42   5.547%   $181.9841   $181.98   $182.00   $182.00  
  7 purchase totals = $1,021.76       $1,106.7193   $1,106.72   $1,106.70   $1,106.80