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 $187.50   8.225%   $202.9219   $202.92   $202.90   $202.90  
  Purchase #2 $217.94   12.859%   $245.9649   $245.96   $245.95   $246.00  
  Purchase #3 $6.87   13.363%   $7.788   $7.79   $7.80   $7.80  
  Purchase #4 $154.84   11.284%   $172.3121   $172.31   $172.30   $172.30  
  Purchase #5 $11.50   11.585%   $12.8323   $12.83   $12.85   $12.80  
  Purchase #6 $250.58   6.334%   $266.4517   $266.45   $266.45   $266.50  
  Purchase #7 $155.72   13.786%   $177.1876   $177.19   $177.20   $177.20  
  7 purchase totals = $984.95       $1,085.4585   $1,085.45   $1,085.45   $1,085.50