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 $159.54   10.276%   $175.9343   $175.93   $175.95   $175.90  
  Purchase #2 $219.64   5.514%   $231.7509   $231.75   $231.75   $231.80  
  Purchase #3 $114.64   10.559%   $126.7448   $126.74   $126.75   $126.70  
  Purchase #4 $177.36   7.810%   $191.2118   $191.21   $191.20   $191.20  
  Purchase #5 $189.80   11.598%   $211.813   $211.81   $211.80   $211.80  
  Purchase #6 $41.88   6.453%   $44.5825   $44.58   $44.60   $44.60  
  Purchase #7 $45.40   4.168%   $47.2923   $47.29   $47.30   $47.30  
  7 purchase totals = $948.26       $1,029.3296   $1,029.31   $1,029.35   $1,029.30