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 $114.76   13.841%   $130.6439   $130.64   $130.65   $130.60  
  Purchase #2 $166.80   3.459%   $172.5696   $172.57   $172.55   $172.60  
  Purchase #3 $109.55   9.849%   $120.3396   $120.34   $120.35   $120.30  
  Purchase #4 $88.55   8.765%   $96.3114   $96.31   $96.30   $96.30  
  Purchase #5 $121.55   4.146%   $126.5895   $126.59   $126.60   $126.60  
  Purchase #6 $103.77   4.616%   $108.56   $108.56   $108.55   $108.60  
  Purchase #7 $238.31   13.158%   $269.6668   $269.67   $269.65   $269.70  
  7 purchase totals = $943.29       $1,024.6808   $1,024.68   $1,024.65   $1,024.70