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 $206.74   10.737%   $228.9377   $228.94   $228.95   $228.90  
  Purchase #2 $231.86   12.797%   $261.5311   $261.53   $261.55   $261.50  
  Purchase #3 $18.70   12.107%   $20.964   $20.96   $20.95   $21.00  
  Purchase #4 $230.83   5.693%   $243.9712   $243.97   $243.95   $244.00  
  Purchase #5 $219.53   8.591%   $238.3898   $238.39   $238.40   $238.40  
  Purchase #6 $49.66   3.782%   $51.5381   $51.54   $51.55   $51.50  
  Purchase #7 $65.32   8.604%   $70.9401   $70.94   $70.95   $70.90  
  7 purchase totals = $1,022.64       $1,116.2720   $1,116.27   $1,116.30   $1,116.20