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 $228.83   10.136%   $252.0242   $252.02   $252.00   $252.00  
  Purchase #2 $151.51   7.426%   $162.7611   $162.76   $162.75   $162.80  
  Purchase #3 $55.49   9.415%   $60.7144   $60.71   $60.70   $60.70  
  Purchase #4 $140.42   7.249%   $150.599   $150.60   $150.60   $150.60  
  Purchase #5 $53.70   11.637%   $59.9491   $59.95   $59.95   $59.90  
  Purchase #6 $209.26   5.504%   $220.7777   $220.78   $220.80   $220.80  
  Purchase #7 $147.72   5.797%   $156.2833   $156.28   $156.30   $156.30  
  7 purchase totals = $986.93       $1,063.1088   $1,063.10   $1,063.10   $1,063.10