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 $32.78   9.115%   $35.7679   $35.77   $35.75   $35.80  
  Purchase #2 $241.87   13.782%   $275.2045   $275.20   $275.20   $275.20  
  Purchase #3 $176.96   6.225%   $187.9758   $187.98   $188.00   $188.00  
  Purchase #4 $61.94   12.818%   $69.8795   $69.88   $69.90   $69.90  
  Purchase #5 $138.44   10.530%   $153.0177   $153.02   $153.00   $153.00  
  Purchase #6 $231.74   13.417%   $262.8326   $262.83   $262.85   $262.80  
  Purchase #7 $124.62   10.852%   $138.1438   $138.14   $138.15   $138.10  
  7 purchase totals = $1,008.35       $1,122.8218   $1,122.82   $1,122.85   $1,122.80