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 $170.93   8.782%   $185.9411   $185.94   $185.95   $185.90  
  Purchase #2 $138.65   6.703%   $147.9437   $147.94   $147.95   $147.90  
  Purchase #3 $181.90   8.288%   $196.9759   $196.98   $197.00   $197.00  
  Purchase #4 $231.66   5.431%   $244.2415   $244.24   $244.25   $244.20  
  Purchase #5 $30.63   6.366%   $32.5799   $32.58   $32.60   $32.60  
  Purchase #6 $111.49   13.295%   $126.3126   $126.31   $126.30   $126.30  
  Purchase #7 $92.74   7.197%   $99.4145   $99.41   $99.40   $99.40  
  7 purchase totals = $958.00       $1,033.4092   $1,033.40   $1,033.45   $1,033.30